Go 1.27 improves HTTP/1 connection reuse performance

Brief written by the FOSSWire AI editor from The Go Blog How we write

October 14, 2026 1 min read 37 reads

Key Takeaway

Go 1.27 significantly reduces the cost of unread HTTP/1 response bodies by improving connection reuse mechanics.

Summary

The Go programming language's net/http package has seen a major performance boost in Go 1.27 regarding HTTP/1 connection reuse. Previously, in Go 1.26 and earlier, failing to fully read an HTTP/1 response body caused the client to abandon the TCP connection, forcing a new handshake for subsequent requests. Go 1.27 addresses this, resulting in up to a fivefold speed increase in specific benchmarks.

Solving the unread body problem

In HTTP/1, responses are sent sequentially; the client cannot find the start of the next response until the current body is fully consumed.
Prior to Go 1.27, calling resp.Body.Close() on an unread body caused net/http to discard the connection.
This issue often occurred when using encoding/json.Decoder, which may leave trailing bytes like newlines unread.
Benchmarks show 100 requests to index.golang.org dropped from ~710ms in Go 1.26 to ~150ms in Go 1.27 when using HTTP/1.

Why it matters

This change prevents silent performance degradation in Go applications that interact with APIs without fully consuming response bodies.

Original reference: go.dev →