WIP 5

overlookmotel · Sep 22, 2019 · fef31d7 · fef31d7
1 parent 8ee53dc
commit fef31d7
Showing 1 changed file with 58 additions and 41 deletions.
diff --git a/lib/index.js b/lib/index.js
@@ -164,54 +164,71 @@ class ChopStream extends Writable {
 			throw new Error('`._read()` called on output stream which has already ended');
 		}
 
+		// TODO Is this required? Currently how many bytes is requested is ignored
 		this._outReadBytes += bytes;
 
-		// Push any content from buffer
-		const {bufferEnd, _outEnd: outEnd} = this;
-		let outPos = this._outPos;
-		if (bufferEnd > outPos) {
-			let chunkStart = this.bufferStart;
+		// If no content in buffer to push, flag stream as flowing so future writes
+		// are pushed to output stream and exit
+		const {bufferEnd, _outPos: outPos} = this;
+		if (bufferEnd <= outPos) {
+			this._outFlowing = true;
+			return;
+		}
 
-			// Error if gap between what's requested and what's in buffer
-			if (chunkStart > outPos) {
-				throw new Error(`Buffer starts at ${chunkStart} but need from ${outPos}`);
-			}
+		// Error if gap between what's requested and what's in buffer
+		let chunkStart = this.bufferStart;
+		if (chunkStart > outPos) {
+			throw new Error(`Buffer starts at ${chunkStart} but need from ${outPos}`);
+		}
 
-			// Push chunks from buffer
-			for (let chunk of this._buffers) {
-				let chunkLength = chunk.length,
-					chunkEnd = chunkStart + chunkLength;
-
-				// If chunk is before desired, skip
-				if (chunkEnd <= outPos) {
-					chunkStart += chunkLength;
-					continue;
-				}
-
-				// If chunk only wanted in part, cut down to just part wanted
-				if (chunkEnd > outEnd) {
-					// Want start of chunk only
-					chunkLength = outEnd - chunkStart;
-					chunkEnd = outEnd;
-					chunk = chunk.slice(0, chunkLength);
-				} else if (chunkStart < outPos) {
-					// Want end of chunk only
-					const splitAt = outPos - chunkStart;
-					chunkLength -= splitAt;
-					chunkStart = outPos;
-					chunk = chunk.slice(splitAt);
-				}
-
-				// Push chunk
-				const flowing = this._pushChunk(chunk);
-				if (!flowing) return;
-				chunkStart += chunkLength;
-				outPos += chunkLength;
+		// Locate first chunk from buffer to push
+		// TODO This loop can be avoided by caching `index` between calls to `._readChunk()`
+		const {_outEnd: outEnd, _buffers: buffers} = this;
+		let index = 0,
+			chunk,
+			chunkEnd;
+		while (true) { // eslint-disable-line no-constant-condition
+			// Get next chunk from buffer
+			chunk = buffers[index];
+			chunkEnd = chunkStart + chunk.length;
+
+			// Stop searching if found first chunk
+			if (chunkStart === outPos) break;
+
+			// Skip chunk if before what's wanted
+			if (chunkEnd <= outPos) {
+				chunkStart = chunkEnd;
+				index++;
+				// NB No need to check if index is out of bounds as already checked above
+				// that buffer does contain data that's wanted
+				continue;
 			}
+
+			// Only part of chunk wanted - split off only what's required
+			chunk = chunk.slice(outPos - chunkStart);
+			chunkStart = outPos;
 		}
 
-		// Flag stream as flowing so future writes are pushed to output stream
-		this._outFlowing = true;
+		// Push chunks
+		while (true) { // eslint-disable-line no-constant-condition
+			// If only part of chunk required, split it
+			if (chunkEnd > outEnd) {
+				chunkEnd = outEnd;
+				chunk = chunk.slice(0, outEnd - chunkStart);
+			}
+
+			// Push chunk
+			const flowing = this._pushChunk(chunk);
+			if (!flowing) break;
+
+			// Get next chunk from buffer
+			index++;
+			if (index === buffers.length) break;
+
+			chunkStart = chunkEnd;
+			chunk = buffers[index];
+			chunkEnd = chunkStart + chunk.length;
+		}
 	}
 
 	/**