node/http: get block header by hash/height

lib/node/http.js

@@ -255,6 +255,23 @@ class HTTP extends Server {
       res.json(200, block.getJSON(this.network, view, height, depth));
     });
 
+    // Block Header by hash/height
+    this.get('/header/:block', async (req, res) => {
+      const valid = Validator.fromRequest(req);
+      const hash = valid.uintbrhash('block');
+
+      enforce(hash != null, 'Hash or height required.');
+
+      const entry = await this.chain.getEntry(hash);
+
+      if (!entry) {
+        res.json(404);
+        return;
+      }
+
+      res.json(200, entry.toJSON());
+    });
+
     // Mempool snapshot
     this.get('/mempool', async (req, res) => {
       enforce(this.mempool, 'No mempool available.');

test/http-test.js

@@ -454,6 +454,50 @@ describe('HTTP', function() {
     assert.strictEqual(blocks.length, 10);
   });
 
+  // depends on the previous test to generate blocks
+  it('should fetch block header', async () => {
+    // fetch corresponding header and block
+    const header = await nclient.get(`/header/${7}`);
+    assert.equal(header.height, 7);
+
+    const properties = [
+      'hash', 'version', 'prevBlock',
+      'merkleRoot', 'time', 'bits',
+      'nonce', 'height', 'chainwork'
+    ];
+
+    for (const property of properties)
+      assert(property in header);
+
+    const block = await nclient.getBlock(7);
+
+    assert.equal(block.hash, header.hash);
+    assert.equal(block.height, header.height);
+    assert.equal(block.version, header.version);
+    assert.equal(block.prevBlock, header.prevBlock);
+    assert.equal(block.merkleRoot, header.merkleRoot);
+    assert.equal(block.time, header.time);
+    assert.equal(block.bits, header.bits);
+    assert.equal(block.nonce, header.nonce);
+  });
+
+  it('should fetch null for block header that does not exist', async () => {
+    // many blocks in the future
+    const header = await nclient.get(`/header/${40000}`);
+    assert.equal(header, null);
+  });
+
+  it('should have valid header chain', async () => {
+    // starting at the genesis block
+    let prevBlock = '0000000000000000000000000000000000000000000000000000000000000000';
+    for (let i = 0; i < 10; i++) {
+      const header = await nclient.get(`/header/${i}`);
+
+      assert.equal(prevBlock, header.prevBlock);
+      prevBlock = header.hash;
+    }
+  });
+
   it('should initiate rescan from socket without a bloom filter', async () => {
     // Rescan from height 5. Without a filter loaded = no response, but no error
     const response = await nclient.call('rescan', 5);