Merge pull request #3714 from obsidiansystems/add-body-to-network-errors

Add response body to network errors

src/libstore/filetransfer.cc

@@ -124,7 +124,7 @@ struct curlFileTransfer : public FileTransfer
             if (requestHeaders) curl_slist_free_all(requestHeaders);
             try {
                 if (!done)
-                    fail(FileTransferError(Interrupted, "download of '%s' was interrupted", request.uri));
+                    fail(FileTransferError(Interrupted, nullptr, "download of '%s' was interrupted", request.uri));
             } catch (...) {
                 ignoreException();
             }
@@ -145,6 +145,7 @@ struct curlFileTransfer : public FileTransfer
 
         LambdaSink finalSink;
         std::shared_ptr<CompressionSink> decompressionSink;
+        std::optional<StringSink> errorSink;
 
         std::exception_ptr writeException;
 
@@ -154,9 +155,19 @@ struct curlFileTransfer : public FileTransfer
                 size_t realSize = size * nmemb;
                 result.bodySize += realSize;
 
-                if (!decompressionSink)
+                if (!decompressionSink) {
                     decompressionSink = makeDecompressionSink(encoding, finalSink);
+                    if (! successfulStatuses.count(getHTTPStatus())) {
+                        // In this case we want to construct a TeeSink, to keep
+                        // the response around (which we figure won't be big
+                        // like an actual download should be) to improve error
+                        // messages.
+                        errorSink = StringSink { };
+                    }
+                }
 
+                if (errorSink)
+                    (*errorSink)((unsigned char *) contents, realSize);
                 (*decompressionSink)((unsigned char *) contents, realSize);
 
                 return realSize;
@@ -412,16 +423,21 @@ struct curlFileTransfer : public FileTransfer
 
                 attempt++;
 
+                std::shared_ptr<std::string> response;
+                if (errorSink)
+                    response = errorSink->s;
                 auto exc =
                     code == CURLE_ABORTED_BY_CALLBACK && _isInterrupted
-                    ? FileTransferError(Interrupted, fmt("%s of '%s' was interrupted", request.verb(), request.uri))
+                    ? FileTransferError(Interrupted, response, "%s of '%s' was interrupted", request.verb(), request.uri)
                     : httpStatus != 0
                     ? FileTransferError(err,
+                        response,
                         fmt("unable to %s '%s': HTTP error %d ('%s')",
                             request.verb(), request.uri, httpStatus, statusMsg)
                         + (code == CURLE_OK ? "" : fmt(" (curl error: %s)", curl_easy_strerror(code)))
                         )
                     : FileTransferError(err,
+                        response,
                         fmt("unable to %s '%s': %s (%d)",
                             request.verb(), request.uri, curl_easy_strerror(code), code));
 
@@ -679,7 +695,7 @@ struct curlFileTransfer : public FileTransfer
                 auto s3Res = s3Helper.getObject(bucketName, key);
                 FileTransferResult res;
                 if (!s3Res.data)
-                    throw FileTransferError(NotFound, fmt("S3 object '%s' does not exist", request.uri));
+                    throw FileTransferError(NotFound, nullptr, "S3 object '%s' does not exist", request.uri);
                 res.data = s3Res.data;
                 callback(std::move(res));
 #else
@@ -824,6 +840,21 @@ void FileTransfer::download(FileTransferRequest && request, Sink & sink)
     }
 }
 
+template<typename... Args>
+FileTransferError::FileTransferError(FileTransfer::Error error, std::shared_ptr<string> response, const Args & ... args)
+    : Error(args...), error(error), response(response)
+{
+    const auto hf = hintfmt(args...);
+    // FIXME: Due to https://github.com/NixOS/nix/issues/3841 we don't know how
+    // to print different messages for different verbosity levels. For now
+    // we add some heuristics for detecting when we want to show the response.
+    if (response && (response->size() < 1024 || response->find("<html>") != string::npos)) {
+            err.hint = hintfmt("%1%\n\nresponse body:\n\n%2%", normaltxt(hf.str()), *response);
+    } else {
+        err.hint = hf;
+    }
+}
+
 bool isUri(const string & s)
 {
     if (s.compare(0, 8, "channel:") == 0) return true;

src/libstore/filetransfer.hh

@@ -103,10 +103,12 @@ class FileTransferError : public Error
 {
 public:
     FileTransfer::Error error;
+    std::shared_ptr<string> response; // intentionally optional
+
     template<typename... Args>
-    FileTransferError(FileTransfer::Error error, const Args & ... args)
-        : Error(args...), error(error)
-    { }
+    FileTransferError(FileTransfer::Error error, std::shared_ptr<string> response, const Args & ... args);
+
+    virtual const char* sname() const override { return "FileTransferError"; }
 };
 
 bool isUri(const string & s);