Rename and protect `BufferedSink::write`

The `write` name is ambiguous and could lead to some funny bugs like
https://github.com/NixOS/nix/pull/8173#issuecomment-1500009480. So
rename it to the more explicit `writeUnbuffered`.
Besides, this method shouldn't be (and isn't) used outside of the class
implementation, so mark it `protected`.

This makes it more symetrical to `BufferedSource` which uses a
`protected readUnbuffered` method.

src/libutil/compression.cc

@@ -23,7 +23,7 @@ struct ChunkedCompressionSink : CompressionSink
 {
     uint8_t outbuf[32 * 1024];
 
-    void write(std::string_view data) override
+    void writeUnbuffered(std::string_view data) override
     {
         const size_t CHUNK_SIZE = sizeof(outbuf) << 2;
         while (!data.empty()) {
@@ -103,7 +103,7 @@ struct ArchiveCompressionSink : CompressionSink
             throw Error(reason, archive_error_string(this->archive));
     }
 
-    void write(std::string_view data) override
+    void writeUnbuffered(std::string_view data) override
     {
         ssize_t result = archive_write_data(archive, data.data(), data.length());
         if (result <= 0) check(result);
@@ -136,7 +136,7 @@ struct NoneSink : CompressionSink
             warn("requested compression level '%d' not supported by compression method 'none'", level);
     }
     void finish() override { flush(); }
-    void write(std::string_view data) override { nextSink(data); }
+    void writeUnbuffered(std::string_view data) override { nextSink(data); }
 };
 
 struct BrotliDecompressionSink : ChunkedCompressionSink

src/libutil/compression.hh

@@ -12,7 +12,7 @@ namespace nix {
 struct CompressionSink : BufferedSink, FinishSink
 {
     using BufferedSink::operator ();
-    using BufferedSink::write;
+    using BufferedSink::writeUnbuffered;
     using FinishSink::finish;
 };
 

src/libutil/hash.cc

@@ -343,7 +343,7 @@ HashSink::~HashSink()
     delete ctx;
 }
 
-void HashSink::write(std::string_view data)
+void HashSink::writeUnbuffered(std::string_view data)
 {
     bytes += data.size();
     update(ht, *ctx, data);

src/libutil/hash.hh

@@ -197,7 +197,7 @@ public:
     HashSink(HashType ht);
     HashSink(const HashSink & h);
     ~HashSink();
-    void write(std::string_view data) override;
+    void writeUnbuffered(std::string_view data) override;
     HashResult finish() override;
     HashResult currentHash();
 };

src/libutil/serialise.cc

@@ -20,7 +20,7 @@ void BufferedSink::operator () (std::string_view data)
            buffer size. */
         if (bufPos + data.size() >= bufSize) {
             flush();
-            write(data);
+            writeUnbuffered(data);
             break;
         }
         /* Otherwise, copy the bytes to the buffer.  Flush the buffer
@@ -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});
+    writeUnbuffered({buffer.get(), n});
 }
 
 
@@ -48,7 +48,7 @@ FdSink::~FdSink()
 }
 
 
-void FdSink::write(std::string_view data)
+void FdSink::writeUnbuffered(std::string_view data)
 {
     written += data.size();
     try {

src/libutil/serialise.hh

@@ -53,7 +53,9 @@ struct BufferedSink : virtual Sink
 
     void flush();
 
-    virtual void write(std::string_view data) = 0;
+protected:
+
+    virtual void writeUnbuffered(std::string_view data) = 0;
 };
 
 
@@ -133,7 +135,7 @@ struct FdSink : BufferedSink
 
     ~FdSink();
 
-    void write(std::string_view data) override;
+    void writeUnbuffered(std::string_view data) override;
 
     bool good() override;
 
@@ -520,7 +522,7 @@ struct FramedSink : nix::BufferedSink
         }
     }
 
-    void write(std::string_view data) override
+    void writeUnbuffered(std::string_view data) override
     {
         /* Don't send more data if the remote has
             encountered an error. */