request: overwrite Content-Length if possible

Also reorganize header normalization

src/index.js

@@ -44,10 +44,6 @@ export default function fetch(url, opts) {
 			throw new Error('only absolute urls are supported');
 		}
 
-		if (options.protocol !== 'http:' && options.protocol !== 'https:') {
-			throw new Error('only http(s) protocols are supported');
-		}
-
 		const send = (options.protocol === 'https:' ? https : http).request;
 
 		// http.request only support string as host header, this hack make custom host header possible

src/request.js

@@ -57,7 +57,7 @@ export default class Request extends Body {
 		});
 
 		// fetch spec options
-		this.method = method;
+		this.method = method.toUpperCase();
 		this.redirect = init.redirect || input.redirect || 'follow';
 		this.headers = new Headers(init.headers || input.headers || {});
 
@@ -79,7 +79,6 @@ export default class Request extends Body {
 		this.agent = init.agent || input.agent;
 
 		this[PARSED_URL] = parsedURL;
-
 		Object.defineProperty(this, Symbol.toStringTag, {
 			value: 'Request',
 			writable: false,
@@ -109,39 +108,53 @@ Object.defineProperty(Request.prototype, Symbol.toStringTag, {
 	configurable: true
 });
 
-function normalizeHeaders(request) {
+export function getNodeRequestOptions(request) {
 	const headers = new Headers(request.headers);
 
-	if (request.compress) {
-		headers.set('accept-encoding', 'gzip,deflate');
+	// fetch step 3
+	if (!headers.has('Accept')) {
+		headers.set('Accept', '*/*');
 	}
 
-	if (!headers.has('user-agent')) {
-		headers.set('user-agent', 'node-fetch/1.0 (+https://github.com/bitinn/node-fetch)');
+	// Basic fetch
+	if (!/^https?:$/.test(request[PARSED_URL].protocol)) {
+		throw new Error('only http(s) protocols are supported');
 	}
 
-	if (!headers.has('connection') && !request.agent) {
-		headers.set('connection', 'close');
+	// HTTP-network-or-cache fetch steps 5-9
+	let contentLengthValue = null;
+	if (request.body == null && /^(POST|PUT)$/i.test(request.method)) {
+		contentLengthValue = '0';
 	}
-
-	if (!headers.has('accept')) {
-		headers.set('accept', '*/*');
-	}
-
-	if (!headers.has('content-length') && /post|put|patch|delete/i.test(request.method)) {
+	if (request.body != null) {
 		const totalBytes = getTotalBytes(request);
 		if (typeof totalBytes === 'number') {
-			headers.set('content-length', totalBytes);
+			contentLengthValue = String(totalBytes);
 		}
 	}
+	if (contentLengthValue) {
+		headers.set('Content-Length', contentLengthValue);
+	}
 
-	return headers;
-}
+	// HTTP-network-or-cache fetch step 12
+	if (!headers.has('User-Agent')) {
+		headers.set('User-Agent', 'node-fetch/1.0 (+https://github.com/bitinn/node-fetch)');
+	}
+
+	// HTTP-network-or-cache fetch step 16
+	if (request.compress) {
+		headers.set('Accept-Encoding', 'gzip,deflate');
+	}
+	if (!headers.has('Connection') && !request.agent) {
+		headers.set('Connection', 'close');
+	}
+
+	// HTTP-network fetch step 4
+	// chunked encoding is handled by Node.js
 
-export function getNodeRequestOptions(request) {
 	return Object.assign({}, request[PARSED_URL], {
 		method: request.method,
-		headers: normalizeHeaders(request).raw(),
+		headers: headers.raw(),
 		agent: request.agent
 	});
 }

test/test.js

@@ -849,6 +849,27 @@ describe('node-fetch', () => {
 		});
 	});
 
+	it('should overwrite Content-Length if possible', function() {
+		url = `${base}inspect`;
+		// note that fetch simply calls tostring on an object
+		opts = {
+			method: 'POST',
+			headers: {
+				'Content-Length': '1000'
+			},
+			body: 'a=1'
+		};
+		return fetch(url, opts).then(res => {
+			return res.json();
+		}).then(res => {
+			expect(res.method).to.equal('POST');
+			expect(res.body).to.equal('a=1');
+			expect(res.headers['transfer-encoding']).to.be.undefined;
+			expect(res.headers['content-type']).to.equal('text/plain;charset=UTF-8');
+			expect(res.headers['content-length']).to.equal('3');
+		});
+	});
+
 	it('should allow PUT request', function() {
 		url = `${base}inspect`;
 		opts = {
@@ -875,22 +896,6 @@ describe('node-fetch', () => {
 		});
 	});
 
-	it('should allow POST request with string body', function() {
-		url = `${base}inspect`;
-		opts = {
-			method: 'POST'
-			, body: 'a=1'
-		};
-		return fetch(url, opts).then(res => {
-			return res.json();
-		}).then(res => {
-			expect(res.method).to.equal('POST');
-			expect(res.body).to.equal('a=1');
-			expect(res.headers['transfer-encoding']).to.be.undefined;
-			expect(res.headers['content-length']).to.equal('3');
-		});
-	});
-
 	it('should allow DELETE request with string body', function() {
 		url = `${base}inspect`;
 		opts = {