Add ContentAddressMethod and parse/render it

src/libstore/content-address.cc

@@ -37,48 +37,86 @@ std::string renderContentAddress(ContentAddress ca) {
     }, ca);
 }
 
-ContentAddress parseContentAddress(std::string_view rawCa) {
-    auto rest = rawCa;
+std::string renderContentAddressMethod(ContentAddressMethod cam) {
+    return std::visit(overloaded {
+        [](TextHashMethod &th) {
+            return std::string{"text:"} + printHashType(htSHA256);
+        },
+        [](FixedOutputHashMethod &fshm) {
+            return "fixed:" + makeFileIngestionPrefix(fshm.fileIngestionMethod) + printHashType(fshm.hashType);
+        }
+    }, cam);
+}
+
+/*
+  Parses content address strings up to the hash.
+ */
+static ContentAddressMethod parseContentAddressMethodPrefix(std::string_view & rest) {
+    std::string wholeInput(rest);
 
     std::string_view prefix;
     {
         auto optPrefix = splitPrefixTo(rest, ':');
         if (!optPrefix)
-            throw UsageError("not a content address because it is not in the form '<prefix>:<rest>': %s", rawCa);
+            throw UsageError("not a content address because it is not in the form '<prefix>:<rest>': %s", wholeInput);
         prefix = *optPrefix;
     }
 
     auto parseHashType_ = [&](){
         auto hashTypeRaw = splitPrefixTo(rest, ':');
         if (!hashTypeRaw)
-            throw UsageError("content address hash must be in form '<algo>:<hash>', but found: %s", rawCa);
+            throw UsageError("content address hash must be in form '<algo>:<hash>', but found: %s", wholeInput);
         HashType hashType = parseHashType(*hashTypeRaw);
         return std::move(hashType);
     };
 
     // Switch on prefix
     if (prefix == "text") {
-        // No parsing of the method, "text" only support flat.
+        // No parsing of the ingestion method, "text" only support flat.
         HashType hashType = parseHashType_();
         if (hashType != htSHA256)
             throw Error("text content address hash should use %s, but instead uses %s",
                 printHashType(htSHA256), printHashType(hashType));
-        return TextHash {
-            .hash = Hash::parseNonSRIUnprefixed(rest, std::move(hashType)),
-        };
+        return TextHashMethod {};
     } else if (prefix == "fixed") {
         // Parse method
         auto method = FileIngestionMethod::Flat;
         if (splitPrefix(rest, "r:"))
             method = FileIngestionMethod::Recursive;
         HashType hashType = parseHashType_();
-        return FixedOutputHash {
-            .method = method,
-            .hash = Hash::parseNonSRIUnprefixed(rest, std::move(hashType)),
+        return FixedOutputHashMethod {
+            .fileIngestionMethod = method,
+            .hashType = std::move(hashType),
         };
     } else
         throw UsageError("content address prefix '%s' is unrecognized. Recogonized prefixes are 'text' or 'fixed'", prefix);
-};
+}
+
+ContentAddress parseContentAddress(std::string_view rawCa) {
+    auto rest = rawCa;
+
+    ContentAddressMethod caMethod = parseContentAddressMethodPrefix(rest);
+
+    return std::visit(
+        overloaded {
+            [&](TextHashMethod thm) {
+                return ContentAddress(TextHash {
+                    .hash = Hash::parseNonSRIUnprefixed(rest, htSHA256)
+                });
+            },
+            [&](FixedOutputHashMethod fohMethod) {
+                return ContentAddress(FixedOutputHash {
+                    .method = fohMethod.fileIngestionMethod,
+                    .hash = Hash::parseNonSRIUnprefixed(rest, std::move(fohMethod.hashType)),
+                });
+            },
+        }, caMethod);
+}
+
+ContentAddressMethod parseContentAddressMethod(std::string_view caMethod) {
+    std::string_view asPrefix {std::string{caMethod} + ":"};
+    return parseContentAddressMethodPrefix(asPrefix);
+}
 
 std::optional<ContentAddress> parseContentAddressOpt(std::string_view rawCaOpt) {
     return rawCaOpt == "" ? std::optional<ContentAddress> {} : parseContentAddress(rawCaOpt);

src/libstore/content-address.hh

@@ -55,4 +55,23 @@ std::optional<ContentAddress> parseContentAddressOpt(std::string_view rawCaOpt);
 
 Hash getContentAddressHash(const ContentAddress & ca);
 
+/*
+  We only have one way to hash text with references, so this is single-value
+  type is only useful in std::variant.
+*/
+struct TextHashMethod { };
+struct FixedOutputHashMethod {
+  FileIngestionMethod fileIngestionMethod;
+  HashType hashType;
+};
+
+typedef std::variant<
+    TextHashMethod,
+    FixedOutputHashMethod
+  > ContentAddressMethod;
+
+ContentAddressMethod parseContentAddressMethod(std::string_view rawCaMethod);
+
+std::string renderContentAddressMethod(ContentAddressMethod caMethod);
+
 }