diff --git a/src/libstore/binary-cache-store.cc b/src/libstore/binary-cache-store.cc
index f6224d6a0..a918b7208 100644
--- a/src/libstore/binary-cache-store.cc
+++ b/src/libstore/binary-cache-store.cc
@@ -86,8 +86,7 @@ void BinaryCacheStore::getFile(const std::string & path, Sink & sink)
                 promise.set_exception(std::current_exception());
             }
         }});
-    auto data = promise.get_future().get();
-    sink((unsigned char *) data->data(), data->size());
+    sink(*promise.get_future().get());
 }
 
 std::shared_ptr<std::string> BinaryCacheStore::getFile(const std::string & path)
diff --git a/src/libstore/build/derivation-goal.cc b/src/libstore/build/derivation-goal.cc
index 76c49f92c..1db85bd37 100644
--- a/src/libstore/build/derivation-goal.cc
+++ b/src/libstore/build/derivation-goal.cc
@@ -916,10 +916,8 @@ void DerivationGoal::buildDone()
 
                 LogSink(Activity & act) : act(act) { }
 
-                void operator() (const unsigned char * data, size_t len) override {
-                    for (size_t i = 0; i < len; i++) {
-                        auto c = data[i];
-
+                void operator() (std::string_view data) override {
+                    for (auto c : data) {
                         if (c == '\n') {
                             flushLine();
                         } else {
@@ -3127,7 +3125,7 @@ void DerivationGoal::registerOutputs()
                     StringSink sink;
                     dumpPath(actualPath, sink);
                     RewritingSink rsink2(oldHashPart, std::string(newInfo0.path.hashPart()), nextSink);
-                    rsink2((unsigned char *) sink.s->data(), sink.s->size());
+                    rsink2(*sink.s);
                     rsink2.flush();
                 });
                 Path tmpPath = actualPath + ".tmp";
diff --git a/src/libstore/daemon.cc b/src/libstore/daemon.cc
index 60cca4fda..cb214bee3 100644
--- a/src/libstore/daemon.cc
+++ b/src/libstore/daemon.cc
@@ -153,10 +153,10 @@ struct TunnelSink : Sink
 {
     Sink & to;
     TunnelSink(Sink & to) : to(to) { }
-    virtual void operator () (const unsigned char * data, size_t len)
+    void operator () (std::string_view data)
     {
         to << STDERR_WRITE;
-        writeString(data, len, to);
+        writeString(data, to);
     }
 };
 
diff --git a/src/libstore/filetransfer.cc b/src/libstore/filetransfer.cc
index c2c65af05..31b4215a9 100644
--- a/src/libstore/filetransfer.cc
+++ b/src/libstore/filetransfer.cc
@@ -95,18 +95,18 @@ struct curlFileTransfer : public FileTransfer
                 fmt(request.data ? "uploading '%s'" : "downloading '%s'", request.uri),
                 {request.uri}, request.parentAct)
             , callback(std::move(callback))
-            , finalSink([this](const unsigned char * data, size_t len) {
+            , finalSink([this](std::string_view data) {
                 if (this->request.dataCallback) {
                     auto httpStatus = getHTTPStatus();
 
                     /* Only write data to the sink if this is a
                        successful response. */
                     if (successfulStatuses.count(httpStatus)) {
-                        writtenToSink += len;
-                        this->request.dataCallback((char *) data, len);
+                        writtenToSink += data.size();
+                        this->request.dataCallback(data);
                     }
                 } else
-                    this->result.data->append((char *) data, len);
+                    this->result.data->append(data);
               })
         {
             if (!request.expectedETag.empty())
@@ -171,8 +171,8 @@ struct curlFileTransfer : public FileTransfer
                 }
 
                 if (errorSink)
-                    (*errorSink)((unsigned char *) contents, realSize);
-                (*decompressionSink)((unsigned char *) contents, realSize);
+                    (*errorSink)({(char *) contents, realSize});
+                (*decompressionSink)({(char *) contents, realSize});
 
                 return realSize;
             } catch (...) {
@@ -776,7 +776,7 @@ void FileTransfer::download(FileTransferRequest && request, Sink & sink)
         state->request.notify_one();
     });
 
-    request.dataCallback = [_state](char * buf, size_t len) {
+    request.dataCallback = [_state](std::string_view data) {
 
         auto state(_state->lock());
 
@@ -794,7 +794,7 @@ void FileTransfer::download(FileTransferRequest && request, Sink & sink)
 
         /* Append data to the buffer and wake up the calling
            thread. */
-        state->data.append(buf, len);
+        state->data.append(data);
         state->avail.notify_one();
     };
 
@@ -840,7 +840,7 @@ void FileTransfer::download(FileTransferRequest && request, Sink & sink)
            if it's blocked on a full buffer. We don't hold the state
            lock while doing this to prevent blocking the download
            thread if sink() takes a long time. */
-        sink((unsigned char *) chunk.data(), chunk.size());
+        sink(chunk);
     }
 }
 
diff --git a/src/libstore/filetransfer.hh b/src/libstore/filetransfer.hh
index c89c51a21..afc7e7aa6 100644
--- a/src/libstore/filetransfer.hh
+++ b/src/libstore/filetransfer.hh
@@ -61,7 +61,7 @@ struct FileTransferRequest
     bool decompress = true;
     std::shared_ptr<std::string> data;
     std::string mimeType;
-    std::function<void(char *, size_t)> dataCallback;
+    std::function<void(std::string_view data)> dataCallback;
 
     FileTransferRequest(const std::string & uri)
         : uri(uri), parentAct(getCurActivity()) { }
diff --git a/src/libstore/nar-accessor.cc b/src/libstore/nar-accessor.cc
index a9efdd0b6..e35031f7a 100644
--- a/src/libstore/nar-accessor.cc
+++ b/src/libstore/nar-accessor.cc
@@ -87,7 +87,7 @@ struct NarAccessor : public FSAccessor
             parents.top()->start = pos;
         }
 
-        void receiveContents(unsigned char * data, size_t len) override
+        void receiveContents(std::string_view data) override
         { }
 
         void createSymlink(const Path & path, const string & target) override
diff --git a/src/libstore/references.cc b/src/libstore/references.cc
index d2096cb49..eb117b5ba 100644
--- a/src/libstore/references.cc
+++ b/src/libstore/references.cc
@@ -55,27 +55,23 @@ struct RefScanSink : Sink
 
     RefScanSink() { }
 
-    void operator () (const unsigned char * data, size_t len);
+    void operator () (std::string_view data) override
+    {
+        /* It's possible that a reference spans the previous and current
+           fragment, so search in the concatenation of the tail of the
+           previous fragment and the start of the current fragment. */
+        string s = tail + std::string(data, 0, refLength);
+        search((const unsigned char *) s.data(), s.size(), hashes, seen);
+
+        search((const unsigned char *) data.data(), data.size(), hashes, seen);
+
+        size_t tailLen = data.size() <= refLength ? data.size() : refLength;
+        tail = std::string(tail, tail.size() < refLength - tailLen ? 0 : tail.size() - (refLength - tailLen));
+        tail.append({data.data() + data.size() - tailLen, tailLen});
+    }
 };
 
 
-void RefScanSink::operator () (const unsigned char * data, size_t len)
-{
-    /* It's possible that a reference spans the previous and current
-       fragment, so search in the concatenation of the tail of the
-       previous fragment and the start of the current fragment. */
-    string s = tail + string((const char *) data, len > refLength ? refLength : len);
-    search((const unsigned char *) s.data(), s.size(), hashes, seen);
-
-    search(data, len, hashes, seen);
-
-    size_t tailLen = len <= refLength ? len : refLength;
-    tail =
-        string(tail, tail.size() < refLength - tailLen ? 0 : tail.size() - (refLength - tailLen)) +
-        string((const char *) data + len - tailLen, tailLen);
-}
-
-
 std::pair<PathSet, HashResult> scanForReferences(const string & path,
     const PathSet & refs)
 {
@@ -129,10 +125,10 @@ RewritingSink::RewritingSink(const std::string & from, const std::string & to, S
     assert(from.size() == to.size());
 }
 
-void RewritingSink::operator () (const unsigned char * data, size_t len)
+void RewritingSink::operator () (std::string_view data)
 {
     std::string s(prev);
-    s.append((const char *) data, len);
+    s.append(data);
 
     size_t j = 0;
     while ((j = s.find(from, j)) != string::npos) {
@@ -146,14 +142,14 @@ void RewritingSink::operator () (const unsigned char * data, size_t len)
 
     pos += consumed;
 
-    if (consumed) nextSink((unsigned char *) s.data(), consumed);
+    if (consumed) nextSink(s.substr(0, consumed));
 }
 
 void RewritingSink::flush()
 {
     if (prev.empty()) return;
     pos += prev.size();
-    nextSink((unsigned char *) prev.data(), prev.size());
+    nextSink(prev);
     prev.clear();
 }
 
@@ -163,9 +159,9 @@ HashModuloSink::HashModuloSink(HashType ht, const std::string & modulus)
 {
 }
 
-void HashModuloSink::operator () (const unsigned char * data, size_t len)
+void HashModuloSink::operator () (std::string_view data)
 {
-    rewritingSink(data, len);
+    rewritingSink(data);
 }
 
 HashResult HashModuloSink::finish()
@@ -176,10 +172,8 @@ HashResult HashModuloSink::finish()
        NAR with self-references and a NAR with some of the
        self-references already zeroed out do not produce a hash
        collision. FIXME: proof. */
-    for (auto & pos : rewritingSink.matches) {
-        auto s = fmt("|%d", pos);
-        hashSink((unsigned char *) s.data(), s.size());
-    }
+    for (auto & pos : rewritingSink.matches)
+        hashSink(fmt("|%d", pos));
 
     auto h = hashSink.finish();
     return {h.first, rewritingSink.pos};
diff --git a/src/libstore/references.hh b/src/libstore/references.hh
index c2efd095c..4f12e6b21 100644
--- a/src/libstore/references.hh
+++ b/src/libstore/references.hh
@@ -19,7 +19,7 @@ struct RewritingSink : Sink
 
     RewritingSink(const std::string & from, const std::string & to, Sink & nextSink);
 
-    void operator () (const unsigned char * data, size_t len) override;
+    void operator () (std::string_view data) override;
 
     void flush();
 };
@@ -31,7 +31,7 @@ struct HashModuloSink : AbstractHashSink
 
     HashModuloSink(HashType ht, const std::string & modulus);
 
-    void operator () (const unsigned char * data, size_t len) override;
+    void operator () (std::string_view data) override;
 
     HashResult finish() override;
 };
diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index 48af9f0c4..6e0c85237 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -857,7 +857,7 @@ std::exception_ptr RemoteStore::Connection::processStderr(Sink * sink, Source *
             if (!source) throw Error("no source");
             size_t len = readNum<size_t>(from);
             auto buf = std::make_unique<unsigned char[]>(len);
-            writeString(buf.get(), source->read(buf.get(), len), to);
+            writeString({(const char *) buf.get(), source->read(buf.get(), len)}, to);
             to.flush();
         }
 
diff --git a/src/libstore/s3-binary-cache-store.cc b/src/libstore/s3-binary-cache-store.cc
index 552c4aac7..4519dd5b5 100644
--- a/src/libstore/s3-binary-cache-store.cc
+++ b/src/libstore/s3-binary-cache-store.cc
@@ -398,7 +398,7 @@ struct S3BinaryCacheStoreImpl : public S3BinaryCacheStore, virtual S3BinaryCache
             printTalkative("downloaded 's3://%s/%s' (%d bytes) in %d ms",
                 bucketName, path, res.data->size(), res.durationMs);
 
-            sink((unsigned char *) res.data->data(), res.data->size());
+            sink(*res.data);
         } else
             throw NoSuchBinaryCacheFile("file '%s' does not exist in binary cache '%s'", path, getUri());
     }
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index 3b2be05cb..27be66cac 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -772,8 +772,8 @@ void copyStorePath(ref<Store> srcStore, ref<Store> dstStore,
     }
 
     auto source = sinkToSource([&](Sink & sink) {
-        LambdaSink progressSink([&](const unsigned char * data, size_t len) {
-            total += len;
+        LambdaSink progressSink([&](std::string_view data) {
+            total += data.size();
             act.progress(total, info->narSize);
         });
         TeeSink tee { sink, progressSink };
diff --git a/src/libutil/archive.cc b/src/libutil/archive.cc
index 03534abc4..046ef841b 100644
--- a/src/libutil/archive.cc
+++ b/src/libutil/archive.cc
@@ -57,7 +57,7 @@ static void dumpContents(const Path & path, size_t size,
         auto n = std::min(left, buf.size());
         readFull(fd.get(), buf.data(), n);
         left -= n;
-        sink(buf.data(), n);
+        sink({(char *) buf.data(), n});
     }
 
     writePadding(size, sink);
@@ -162,7 +162,7 @@ static void parseContents(ParseSink & sink, Source & source, const Path & path)
         auto n = buf.size();
         if ((uint64_t)n > left) n = left;
         source(buf.data(), n);
-        sink.receiveContents(buf.data(), n);
+        sink.receiveContents({(char *) buf.data(), n});
         left -= n;
     }
 
@@ -300,21 +300,21 @@ struct RestoreSink : ParseSink
     Path dstPath;
     AutoCloseFD fd;
 
-    void createDirectory(const Path & path)
+    void createDirectory(const Path & path) override
     {
         Path p = dstPath + path;
         if (mkdir(p.c_str(), 0777) == -1)
             throw SysError("creating directory '%1%'", p);
     };
 
-    void createRegularFile(const Path & path)
+    void createRegularFile(const Path & path) override
     {
         Path p = dstPath + path;
         fd = open(p.c_str(), O_CREAT | O_EXCL | O_WRONLY | O_CLOEXEC, 0666);
         if (!fd) throw SysError("creating file '%1%'", p);
     }
 
-    void isExecutable()
+    void isExecutable() override
     {
         struct stat st;
         if (fstat(fd.get(), &st) == -1)
@@ -323,7 +323,7 @@ struct RestoreSink : ParseSink
             throw SysError("fchmod");
     }
 
-    void preallocateContents(uint64_t len)
+    void preallocateContents(uint64_t len) override
     {
         if (!archiveSettings.preallocateContents)
             return;
@@ -341,12 +341,12 @@ struct RestoreSink : ParseSink
 #endif
     }
 
-    void receiveContents(unsigned char * data, size_t len)
+    void receiveContents(std::string_view data) override
     {
-        writeFull(fd.get(), data, len);
+        writeFull(fd.get(), data);
     }
 
-    void createSymlink(const Path & path, const string & target)
+    void createSymlink(const Path & path, const string & target) override
     {
         Path p = dstPath + path;
         nix::createSymlink(target, p);
diff --git a/src/libutil/archive.hh b/src/libutil/archive.hh
index 5665732d2..fe22435ef 100644
--- a/src/libutil/archive.hh
+++ b/src/libutil/archive.hh
@@ -58,7 +58,7 @@ struct ParseSink
     virtual void createRegularFile(const Path & path) { };
     virtual void isExecutable() { };
     virtual void preallocateContents(uint64_t size) { };
-    virtual void receiveContents(unsigned char * data, size_t len) { };
+    virtual void receiveContents(std::string_view data) { };
 
     virtual void createSymlink(const Path & path, const string & target) { };
 };
@@ -72,14 +72,14 @@ struct RetrieveRegularNARSink : ParseSink
 
     RetrieveRegularNARSink(Sink & sink) : sink(sink) { }
 
-    void createDirectory(const Path & path)
+    void createDirectory(const Path & path) override
     {
         regular = false;
     }
 
-    void receiveContents(unsigned char * data, size_t len)
+    void receiveContents(std::string_view data) override
     {
-        sink(data, len);
+        sink(data);
     }
 
     void createSymlink(const Path & path, const string & target)
diff --git a/src/libutil/compression.cc b/src/libutil/compression.cc
index a117ddc72..986ba2976 100644
--- a/src/libutil/compression.cc
+++ b/src/libutil/compression.cc
@@ -22,18 +22,17 @@ struct ChunkedCompressionSink : CompressionSink
 {
     uint8_t outbuf[32 * 1024];
 
-    void write(const unsigned char * data, size_t len) override
+    void write(std::string_view data) override
     {
         const size_t CHUNK_SIZE = sizeof(outbuf) << 2;
-        while (len) {
-            size_t n = std::min(CHUNK_SIZE, len);
-            writeInternal(data, n);
-            data += n;
-            len -= n;
+        while (!data.empty()) {
+            size_t n = std::min(CHUNK_SIZE, data.size());
+            writeInternal(data);
+            data.remove_prefix(n);
         }
     }
 
-    virtual void writeInternal(const unsigned char * data, size_t len) = 0;
+    virtual void writeInternal(std::string_view data) = 0;
 };
 
 struct NoneSink : CompressionSink
@@ -41,7 +40,7 @@ struct NoneSink : CompressionSink
     Sink & nextSink;
     NoneSink(Sink & nextSink) : nextSink(nextSink) { }
     void finish() override { flush(); }
-    void write(const unsigned char * data, size_t len) override { nextSink(data, len); }
+    void write(std::string_view data) override { nextSink(data); }
 };
 
 struct GzipDecompressionSink : CompressionSink
@@ -75,28 +74,28 @@ struct GzipDecompressionSink : CompressionSink
     void finish() override
     {
         CompressionSink::flush();
-        write(nullptr, 0);
+        write({});
     }
 
-    void write(const unsigned char * data, size_t len) override
+    void write(std::string_view data) override
     {
-        assert(len <= std::numeric_limits<decltype(strm.avail_in)>::max());
+        assert(data.size() <= std::numeric_limits<decltype(strm.avail_in)>::max());
 
-        strm.next_in = (Bytef *) data;
-        strm.avail_in = len;
+        strm.next_in = (Bytef *) data.data();
+        strm.avail_in = data.size();
 
-        while (!finished && (!data || strm.avail_in)) {
+        while (!finished && (!data.data() || strm.avail_in)) {
             checkInterrupt();
 
             int ret = inflate(&strm,Z_SYNC_FLUSH);
             if (ret != Z_OK && ret != Z_STREAM_END)
                 throw CompressionError("error while decompressing gzip file: %d (%d, %d)",
-                    zError(ret), len, strm.avail_in);
+                    zError(ret), data.size(), strm.avail_in);
 
             finished = ret == Z_STREAM_END;
 
             if (strm.avail_out < sizeof(outbuf) || strm.avail_in == 0) {
-                nextSink(outbuf, sizeof(outbuf) - strm.avail_out);
+                nextSink({(char *) outbuf, sizeof(outbuf) - strm.avail_out});
                 strm.next_out = (Bytef *) outbuf;
                 strm.avail_out = sizeof(outbuf);
             }
@@ -130,25 +129,25 @@ struct XzDecompressionSink : CompressionSink
     void finish() override
     {
         CompressionSink::flush();
-        write(nullptr, 0);
+        write({});
     }
 
-    void write(const unsigned char * data, size_t len) override
+    void write(std::string_view data) override
     {
-        strm.next_in = data;
-        strm.avail_in = len;
+        strm.next_in = (const unsigned char *) data.data();
+        strm.avail_in = data.size();
 
-        while (!finished && (!data || strm.avail_in)) {
+        while (!finished && (!data.data() || strm.avail_in)) {
             checkInterrupt();
 
-            lzma_ret ret = lzma_code(&strm, data ? LZMA_RUN : LZMA_FINISH);
+            lzma_ret ret = lzma_code(&strm, data.data() ? LZMA_RUN : LZMA_FINISH);
             if (ret != LZMA_OK && ret != LZMA_STREAM_END)
                 throw CompressionError("error %d while decompressing xz file", ret);
 
             finished = ret == LZMA_STREAM_END;
 
             if (strm.avail_out < sizeof(outbuf) || strm.avail_in == 0) {
-                nextSink(outbuf, sizeof(outbuf) - strm.avail_out);
+                nextSink({(char *) outbuf, sizeof(outbuf) - strm.avail_out});
                 strm.next_out = outbuf;
                 strm.avail_out = sizeof(outbuf);
             }
@@ -181,15 +180,15 @@ struct BzipDecompressionSink : ChunkedCompressionSink
     void finish() override
     {
         flush();
-        write(nullptr, 0);
+        write({});
     }
 
-    void writeInternal(const unsigned char * data, size_t len) override
+    void writeInternal(std::string_view data) override
     {
-        assert(len <= std::numeric_limits<decltype(strm.avail_in)>::max());
+        assert(data.size() <= std::numeric_limits<decltype(strm.avail_in)>::max());
 
-        strm.next_in = (char *) data;
-        strm.avail_in = len;
+        strm.next_in = (char *) data.data();
+        strm.avail_in = data.size();
 
         while (strm.avail_in) {
             checkInterrupt();
@@ -201,7 +200,7 @@ struct BzipDecompressionSink : ChunkedCompressionSink
             finished = ret == BZ_STREAM_END;
 
             if (strm.avail_out < sizeof(outbuf) || strm.avail_in == 0) {
-                nextSink(outbuf, sizeof(outbuf) - strm.avail_out);
+                nextSink({(char *) outbuf, sizeof(outbuf) - strm.avail_out});
                 strm.next_out = (char *) outbuf;
                 strm.avail_out = sizeof(outbuf);
             }
@@ -230,17 +229,17 @@ struct BrotliDecompressionSink : ChunkedCompressionSink
     void finish() override
     {
         flush();
-        writeInternal(nullptr, 0);
+        writeInternal({});
     }
 
-    void writeInternal(const unsigned char * data, size_t len) override
+    void writeInternal(std::string_view data) override
     {
-        const uint8_t * next_in = data;
-        size_t avail_in = len;
+        auto next_in = (const uint8_t *) data.data();
+        size_t avail_in = data.size();
         uint8_t * next_out = outbuf;
         size_t avail_out = sizeof(outbuf);
 
-        while (!finished && (!data || avail_in)) {
+        while (!finished && (!data.data() || avail_in)) {
             checkInterrupt();
 
             if (!BrotliDecoderDecompressStream(state,
@@ -250,7 +249,7 @@ struct BrotliDecompressionSink : ChunkedCompressionSink
                 throw CompressionError("error while decompressing brotli file");
 
             if (avail_out < sizeof(outbuf) || avail_in == 0) {
-                nextSink(outbuf, sizeof(outbuf) - avail_out);
+                nextSink({(char *) outbuf, sizeof(outbuf) - avail_out});
                 next_out = outbuf;
                 avail_out = sizeof(outbuf);
             }
@@ -338,25 +337,25 @@ struct XzCompressionSink : CompressionSink
     void finish() override
     {
         CompressionSink::flush();
-        write(nullptr, 0);
+        write({});
     }
 
-    void write(const unsigned char * data, size_t len) override
+    void write(std::string_view data) override
     {
-        strm.next_in = data;
-        strm.avail_in = len;
+        strm.next_in = (const unsigned char *) data.data();
+        strm.avail_in = data.size();
 
-        while (!finished && (!data || strm.avail_in)) {
+        while (!finished && (!data.data() || strm.avail_in)) {
             checkInterrupt();
 
-            lzma_ret ret = lzma_code(&strm, data ? LZMA_RUN : LZMA_FINISH);
+            lzma_ret ret = lzma_code(&strm, data.data() ? LZMA_RUN : LZMA_FINISH);
             if (ret != LZMA_OK && ret != LZMA_STREAM_END)
                 throw CompressionError("error %d while compressing xz file", ret);
 
             finished = ret == LZMA_STREAM_END;
 
             if (strm.avail_out < sizeof(outbuf) || strm.avail_in == 0) {
-                nextSink(outbuf, sizeof(outbuf) - strm.avail_out);
+                nextSink({(const char *) outbuf, sizeof(outbuf) - strm.avail_out});
                 strm.next_out = outbuf;
                 strm.avail_out = sizeof(outbuf);
             }
@@ -389,27 +388,27 @@ struct BzipCompressionSink : ChunkedCompressionSink
     void finish() override
     {
         flush();
-        writeInternal(nullptr, 0);
+        writeInternal({});
     }
 
-    void writeInternal(const unsigned char * data, size_t len) override
+    void writeInternal(std::string_view data) override
     {
-        assert(len <= std::numeric_limits<decltype(strm.avail_in)>::max());
+        assert(data.size() <= std::numeric_limits<decltype(strm.avail_in)>::max());
 
-        strm.next_in = (char *) data;
-        strm.avail_in = len;
+        strm.next_in = (char *) data.data();
+        strm.avail_in = data.size();
 
-        while (!finished && (!data || strm.avail_in)) {
+        while (!finished && (!data.data() || strm.avail_in)) {
             checkInterrupt();
 
-            int ret = BZ2_bzCompress(&strm, data ? BZ_RUN : BZ_FINISH);
+            int ret = BZ2_bzCompress(&strm, data.data() ? BZ_RUN : BZ_FINISH);
             if (ret != BZ_RUN_OK && ret != BZ_FINISH_OK && ret != BZ_STREAM_END)
                 throw CompressionError("error %d while compressing bzip2 file", ret);
 
             finished = ret == BZ_STREAM_END;
 
             if (strm.avail_out < sizeof(outbuf) || strm.avail_in == 0) {
-                nextSink(outbuf, sizeof(outbuf) - strm.avail_out);
+                nextSink({(const char *) outbuf, sizeof(outbuf) - strm.avail_out});
                 strm.next_out = (char *) outbuf;
                 strm.avail_out = sizeof(outbuf);
             }
@@ -439,28 +438,28 @@ struct BrotliCompressionSink : ChunkedCompressionSink
     void finish() override
     {
         flush();
-        writeInternal(nullptr, 0);
+        writeInternal({});
     }
 
-    void writeInternal(const unsigned char * data, size_t len) override
+    void writeInternal(std::string_view data) override
     {
-        const uint8_t * next_in = data;
-        size_t avail_in = len;
+        auto next_in = (const uint8_t *) data.data();
+        size_t avail_in = data.size();
         uint8_t * next_out = outbuf;
         size_t avail_out = sizeof(outbuf);
 
-        while (!finished && (!data || avail_in)) {
+        while (!finished && (!data.data() || avail_in)) {
             checkInterrupt();
 
             if (!BrotliEncoderCompressStream(state,
-                    data ? BROTLI_OPERATION_PROCESS : BROTLI_OPERATION_FINISH,
+                    data.data() ? BROTLI_OPERATION_PROCESS : BROTLI_OPERATION_FINISH,
                     &avail_in, &next_in,
                     &avail_out, &next_out,
                     nullptr))
                 throw CompressionError("error while compressing brotli compression");
 
             if (avail_out < sizeof(outbuf) || avail_in == 0) {
-                nextSink(outbuf, sizeof(outbuf) - avail_out);
+                nextSink({(const char *) outbuf, sizeof(outbuf) - avail_out});
                 next_out = outbuf;
                 avail_out = sizeof(outbuf);
             }
diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index 8efff190a..4df8b4ecb 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -291,12 +291,12 @@ static void start(HashType ht, Ctx & ctx)
 
 
 static void update(HashType ht, Ctx & ctx,
-    const unsigned char * bytes, size_t len)
+    std::string_view data)
 {
-    if (ht == htMD5) MD5_Update(&ctx.md5, bytes, len);
-    else if (ht == htSHA1) SHA1_Update(&ctx.sha1, bytes, len);
-    else if (ht == htSHA256) SHA256_Update(&ctx.sha256, bytes, len);
-    else if (ht == htSHA512) SHA512_Update(&ctx.sha512, bytes, len);
+    if (ht == htMD5) MD5_Update(&ctx.md5, data.data(), data.size());
+    else if (ht == htSHA1) SHA1_Update(&ctx.sha1, data.data(), data.size());
+    else if (ht == htSHA256) SHA256_Update(&ctx.sha256, data.data(), data.size());
+    else if (ht == htSHA512) SHA512_Update(&ctx.sha512, data.data(), data.size());
 }
 
 
@@ -314,7 +314,7 @@ Hash hashString(HashType ht, std::string_view s)
     Ctx ctx;
     Hash hash(ht);
     start(ht, ctx);
-    update(ht, ctx, (const unsigned char *) s.data(), s.length());
+    update(ht, ctx, s);
     finish(ht, ctx, hash.hash);
     return hash;
 }
@@ -341,10 +341,10 @@ HashSink::~HashSink()
     delete ctx;
 }
 
-void HashSink::write(const unsigned char * data, size_t len)
+void HashSink::write(std::string_view data)
 {
-    bytes += len;
-    update(ht, *ctx, data, len);
+    bytes += data.size();
+    update(ht, *ctx, data);
 }
 
 HashResult HashSink::finish()
diff --git a/src/libutil/hash.hh b/src/libutil/hash.hh
index 6d6eb70ca..1b626dd85 100644
--- a/src/libutil/hash.hh
+++ b/src/libutil/hash.hh
@@ -156,7 +156,7 @@ public:
     HashSink(HashType ht);
     HashSink(const HashSink & h);
     ~HashSink();
-    void write(const unsigned char * data, size_t len) override;
+    void write(std::string_view data) override;
     HashResult finish() override;
     HashResult currentHash();
 };
diff --git a/src/libutil/serialise.cc b/src/libutil/serialise.cc
index 038ede049..534ad5cbb 100644
--- a/src/libutil/serialise.cc
+++ b/src/libutil/serialise.cc
@@ -11,23 +11,23 @@
 namespace nix {
 
 
-void BufferedSink::operator () (const unsigned char * data, size_t len)
+void BufferedSink::operator () (std::string_view data)
 {
-    if (!buffer) buffer = decltype(buffer)(new unsigned char[bufSize]);
+    if (!buffer) buffer = decltype(buffer)(new char[bufSize]);
 
-    while (len) {
+    while (!data.empty()) {
         /* Optimisation: bypass the buffer if the data exceeds the
            buffer size. */
-        if (bufPos + len >= bufSize) {
+        if (bufPos + data.size() >= bufSize) {
             flush();
-            write(data, len);
+            write(data);
             break;
         }
         /* Otherwise, copy the bytes to the buffer.  Flush the buffer
            when it's full. */
-        size_t n = bufPos + len > bufSize ? bufSize - bufPos : len;
-        memcpy(buffer.get() + bufPos, data, n);
-        data += n; bufPos += n; len -= n;
+        size_t n = bufPos + data.size() > bufSize ? bufSize - bufPos : data.size();
+        memcpy(buffer.get() + bufPos, data.data(), n);
+        data.remove_prefix(n); bufPos += n;
         if (bufPos == bufSize) flush();
     }
 }
@@ -38,7 +38,7 @@ void BufferedSink::flush()
     if (bufPos == 0) return;
     size_t n = bufPos;
     bufPos = 0; // don't trigger the assert() in ~BufferedSink()
-    write(buffer.get(), n);
+    write({buffer.get(), n});
 }
 
 
@@ -59,9 +59,9 @@ static void warnLargeDump()
 }
 
 
-void FdSink::write(const unsigned char * data, size_t len)
+void FdSink::write(std::string_view data)
 {
-    written += len;
+    written += data.size();
     static bool warned = false;
     if (warn && !warned) {
         if (written > threshold) {
@@ -70,7 +70,7 @@ void FdSink::write(const unsigned char * data, size_t len)
         }
     }
     try {
-        writeFull(fd, data, len);
+        writeFull(fd, data);
     } catch (SysError & e) {
         _good = false;
         throw;
@@ -101,7 +101,7 @@ void Source::drainInto(Sink & sink)
         size_t n;
         try {
             n = read(buf.data(), buf.size());
-            sink(buf.data(), n);
+            sink({(char *) buf.data(), n});
         } catch (EndOfFile &) {
             break;
         }
@@ -229,9 +229,9 @@ std::unique_ptr<Source> sinkToSource(
         {
             if (!coro)
                 coro = coro_t::pull_type(VirtualStackAllocator{}, [&](coro_t::push_type & yield) {
-                    LambdaSink sink([&](const unsigned char * data, size_t len) {
-                            if (len) yield(std::string((const char *) data, len));
-                        });
+                    LambdaSink sink([&](std::string_view data) {
+                        if (!data.empty()) yield(std::string(data));
+                    });
                     fun(sink);
                 });
 
@@ -260,22 +260,22 @@ void writePadding(size_t len, Sink & sink)
     if (len % 8) {
         unsigned char zero[8];
         memset(zero, 0, sizeof(zero));
-        sink(zero, 8 - (len % 8));
+        sink({(char *) zero, 8 - (len % 8)});
     }
 }
 
 
-void writeString(const unsigned char * buf, size_t len, Sink & sink)
+void writeString(std::string_view data, Sink & sink)
 {
-    sink << len;
-    sink(buf, len);
-    writePadding(len, sink);
+    sink << data.size();
+    sink(data);
+    writePadding(data.size(), sink);
 }
 
 
 Sink & operator << (Sink & sink, const string & s)
 {
-    writeString((const unsigned char *) s.data(), s.size(), sink);
+    writeString(s, sink);
     return sink;
 }
 
@@ -394,14 +394,14 @@ Error readError(Source & source)
 }
 
 
-void StringSink::operator () (const unsigned char * data, size_t len)
+void StringSink::operator () (std::string_view data)
 {
     static bool warned = false;
     if (!warned && s->size() > threshold) {
         warnLargeDump();
         warned = true;
     }
-    s->append((const char *) data, len);
+    s->append(data);
 }
 
 size_t ChainSource::read(unsigned char * data, size_t len)
diff --git a/src/libutil/serialise.hh b/src/libutil/serialise.hh
index 5c7d3ce76..f9ab79997 100644
--- a/src/libutil/serialise.hh
+++ b/src/libutil/serialise.hh
@@ -14,19 +14,14 @@ namespace nix {
 struct Sink
 {
     virtual ~Sink() { }
-    virtual void operator () (const unsigned char * data, size_t len) = 0;
+    virtual void operator () (std::string_view data) = 0;
     virtual bool good() { return true; }
-
-    void operator () (const std::string & s)
-    {
-        (*this)((const unsigned char *) s.data(), s.size());
-    }
 };
 
 /* Just throws away data. */
 struct NullSink : Sink
 {
-    void operator () (const unsigned char * data, size_t len) override
+    void operator () (std::string_view data) override
     { }
 };
 
@@ -35,21 +30,16 @@ struct NullSink : Sink
 struct BufferedSink : virtual Sink
 {
     size_t bufSize, bufPos;
-    std::unique_ptr<unsigned char[]> buffer;
+    std::unique_ptr<char[]> buffer;
 
     BufferedSink(size_t bufSize = 32 * 1024)
         : bufSize(bufSize), bufPos(0), buffer(nullptr) { }
 
-    void operator () (const unsigned char * data, size_t len) override;
-
-    void operator () (const std::string & s)
-    {
-        Sink::operator()(s);
-    }
+    void operator () (std::string_view data) override;
 
     void flush();
 
-    virtual void write(const unsigned char * data, size_t len) = 0;
+    virtual void write(std::string_view data) = 0;
 };
 
 
@@ -119,7 +109,7 @@ struct FdSink : BufferedSink
 
     ~FdSink();
 
-    void write(const unsigned char * data, size_t len) override;
+    void write(std::string_view data) override;
 
     bool good() override;
 
@@ -163,7 +153,7 @@ struct StringSink : Sink
       s->reserve(reservedSize);
     };
     StringSink(ref<std::string> s) : s(s) { };
-    void operator () (const unsigned char * data, size_t len) override;
+    void operator () (std::string_view data) override;
 };
 
 
@@ -182,10 +172,10 @@ struct TeeSink : Sink
 {
     Sink & sink1, & sink2;
     TeeSink(Sink & sink1, Sink & sink2) : sink1(sink1), sink2(sink2) { }
-    virtual void operator () (const unsigned char * data, size_t len)
+    virtual void operator () (std::string_view data)
     {
-        sink1(data, len);
-        sink2(data, len);
+        sink1(data);
+        sink2(data);
     }
 };
 
@@ -200,7 +190,7 @@ struct TeeSource : Source
     size_t read(unsigned char * data, size_t len)
     {
         size_t n = orig.read(data, len);
-        sink(data, n);
+        sink({(char *) data, n});
         return n;
     }
 };
@@ -241,24 +231,24 @@ struct LengthSink : Sink
 {
     uint64_t length = 0;
 
-    virtual void operator () (const unsigned char * _, size_t len)
+    void operator () (std::string_view data) override
     {
-        length += len;
+        length += data.size();
     }
 };
 
 /* Convert a function into a sink. */
 struct LambdaSink : Sink
 {
-    typedef std::function<void(const unsigned char *, size_t)> lambda_t;
+    typedef std::function<void(std::string_view data)> lambda_t;
 
     lambda_t lambda;
 
     LambdaSink(const lambda_t & lambda) : lambda(lambda) { }
 
-    virtual void operator () (const unsigned char * data, size_t len)
+    void operator () (std::string_view data) override
     {
-        lambda(data, len);
+        lambda(data);
     }
 };
 
@@ -302,7 +292,7 @@ std::unique_ptr<Source> sinkToSource(
 
 
 void writePadding(size_t len, Sink & sink);
-void writeString(const unsigned char * buf, size_t len, Sink & sink);
+void writeString(std::string_view s, Sink & sink);
 
 inline Sink & operator << (Sink & sink, uint64_t n)
 {
@@ -315,7 +305,7 @@ inline Sink & operator << (Sink & sink, uint64_t n)
     buf[5] = (n >> 40) & 0xff;
     buf[6] = (n >> 48) & 0xff;
     buf[7] = (unsigned char) (n >> 56) & 0xff;
-    sink(buf, sizeof(buf));
+    sink({(char *) buf, sizeof(buf)});
     return sink;
 }
 
@@ -484,7 +474,7 @@ struct FramedSink : nix::BufferedSink
         }
     }
 
-    void write(const unsigned char * data, size_t len) override
+    void write(std::string_view data) override
     {
         /* Don't send more data if the remote has
             encountered an error. */
@@ -493,8 +483,8 @@ struct FramedSink : nix::BufferedSink
             ex = nullptr;
             std::rethrow_exception(ex2);
         }
-        to << len;
-        to(data, len);
+        to << data.size();
+        to(data);
     };
 };
 
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 98a069c3e..3d4fc4c25 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -346,7 +346,7 @@ void writeFile(const Path & path, Source & source, mode_t mode)
         while (true) {
             try {
                 auto n = source.read(buf.data(), buf.size());
-                writeFull(fd.get(), (unsigned char *) buf.data(), n);
+                writeFull(fd.get(), {(char *) buf.data(), n});
             } catch (EndOfFile &) { break; }
         }
     } catch (Error & e) {
@@ -648,24 +648,16 @@ void readFull(int fd, unsigned char * buf, size_t count)
 }
 
 
-void writeFull(int fd, const unsigned char * buf, size_t count, bool allowInterrupts)
-{
-    while (count) {
-        if (allowInterrupts) checkInterrupt();
-        ssize_t res = write(fd, (char *) buf, count);
-        if (res == -1 && errno != EINTR)
-            throw SysError("writing to file");
-        if (res > 0) {
-            count -= res;
-            buf += res;
-        }
-    }
-}
-
-
 void writeFull(int fd, std::string_view s, bool allowInterrupts)
 {
-    writeFull(fd, (const unsigned char *) s.data(), s.size(), allowInterrupts);
+    while (!s.empty()) {
+        if (allowInterrupts) checkInterrupt();
+        ssize_t res = write(fd, s.data(), s.size());
+        if (res == -1 && errno != EINTR)
+            throw SysError("writing to file");
+        if (res > 0)
+            s.remove_prefix(res);
+    }
 }
 
 
@@ -705,7 +697,7 @@ void drainFD(int fd, Sink & sink, bool block)
                 throw SysError("reading from file");
         }
         else if (rd == 0) break;
-        else sink(buf.data(), rd);
+        else sink({(char *) buf.data(), (size_t) rd});
     }
 }
 
@@ -1153,7 +1145,7 @@ void runProgram2(const RunOptions & options)
                     } catch (EndOfFile &) {
                         break;
                     }
-                    writeFull(in.writeSide.get(), buf.data(), n);
+                    writeFull(in.writeSide.get(), {(char *) buf.data(), n});
                 }
                 promise.set_value();
             } catch (...) {
diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index eb872dd4b..fcb7cad39 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -156,7 +156,6 @@ void replaceSymlink(const Path & target, const Path & link,
 /* Wrappers arount read()/write() that read/write exactly the
    requested number of bytes. */
 void readFull(int fd, unsigned char * buf, size_t count);
-void writeFull(int fd, const unsigned char * buf, size_t count, bool allowInterrupts = true);
 void writeFull(int fd, std::string_view s, bool allowInterrupts = true);
 
 MakeError(EndOfFile, Error);
diff --git a/src/nix/make-content-addressable.cc b/src/nix/make-content-addressable.cc
index df3ec5194..12c2cf776 100644
--- a/src/nix/make-content-addressable.cc
+++ b/src/nix/make-content-addressable.cc
@@ -73,7 +73,7 @@ struct CmdMakeContentAddressable : StorePathsCommand, MixJSON
             *sink.s = rewriteStrings(*sink.s, rewrites);
 
             HashModuloSink hashModuloSink(htSHA256, oldHashPart);
-            hashModuloSink((unsigned char *) sink.s->data(), sink.s->size());
+            hashModuloSink(*sink.s);
 
             auto narHash = hashModuloSink.finish().first;
 
@@ -94,7 +94,7 @@ struct CmdMakeContentAddressable : StorePathsCommand, MixJSON
 
             auto source = sinkToSource([&](Sink & nextSink) {
                 RewritingSink rsink2(oldHashPart, std::string(info.path.hashPart()), nextSink);
-                rsink2((unsigned char *) sink.s->data(), sink.s->size());
+                rsink2(*sink.s);
                 rsink2.flush();
             });