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fix: improve SSE stream response handling and add fasthttp support (#888) #1014

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fix: improve SSE stream response handling and add fasthttp support (#888) #1014

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fc65e34
fix: improve SSE stream response handling and add fasthttp support (#…
zhouyusd Apr 14, 2026
dfa7105
fix: handle flush error
zhouyusd Apr 14, 2026
70aa0ab
chore: simplify encoder creation
zhouyusd Apr 14, 2026
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115 changes: 66 additions & 49 deletions sse/sse.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2,9 +2,11 @@
package sse

import (
"bufio"
"context"
"encoding/json"
"fmt"
"io"
"net/http"
"os"
"reflect"
Expand All @@ -14,6 +16,7 @@ import (
"time"

"github.com/danielgtaylor/huma/v2"
"github.com/valyala/fasthttp"
)

// WriteTimeout is the timeout for writing to the client.
Expand Down Expand Up @@ -54,6 +57,14 @@ func (s Sender) Data(data any) error {
return s(Message{Data: data})
}

type flusherFunc func() error

func (f flusherFunc) Flush() {
if err := f(); err != nil {
fmt.Fprintf(os.Stderr, "warning: flush failed: %v\n", err)
}
}

// Register a new SSE operation. The `eventTypeMap` maps from event name to
// the type of the data that will be sent. The `f` function is called with
// the context, input, and a `send` function that can be used to send messages
Expand Down Expand Up @@ -133,8 +144,61 @@ func Register[I any](api huma.API, op huma.Operation, eventTypeMap map[string]an
Body: func(ctx huma.Context) {
ctx.SetHeader("Content-Type", "text/event-stream")
bw := ctx.BodyWriter()
encoder := json.NewEncoder(bw)
send := func(deadliner writeDeadliner, flusher http.Flusher, writer io.Writer) Sender {
encoder := json.NewEncoder(writer)
return func(msg Message) error {
if deadliner != nil {
if err := deadliner.SetWriteDeadline(time.Now().Add(WriteTimeout)); err != nil {
fmt.Fprintf(os.Stderr, "warning: unable to set write deadline: %v\n", err)
}
} else {
fmt.Fprintln(os.Stderr, "write deadline not supported by underlying writer")
}

// Write optional fields
if msg.ID > 0 {
writer.Write(fmt.Appendf(nil, "id: %d\n", msg.ID))
}
if msg.Retry > 0 {
writer.Write(fmt.Appendf(nil, "retry: %d\n", msg.Retry))
}

event, ok := typeToEvent[deref(reflect.TypeOf(msg.Data))]
if !ok {
fmt.Fprintf(os.Stderr, "error: unknown event type %v\n", reflect.TypeOf(msg.Data))
debug.PrintStack()
}
if event != "" && event != "message" {
// `message` is the default, so no need to transmit it.
writer.Write([]byte("event: " + event + "\n"))
}

// Write the message data.
if _, err := writer.Write([]byte("data: ")); err != nil {
return err
}
if err := encoder.Encode(msg.Data); err != nil {
writer.Write([]byte(`{"error": "encode error: `))
writer.Write([]byte(err.Error()))
writer.Write([]byte("\"}\n\n"))
return err
}
writer.Write([]byte("\n"))
if flusher != nil {
flusher.Flush()
} else {
fmt.Fprintln(os.Stderr, "error: unable to flush")
return fmt.Errorf("unable to flush: %w", http.ErrNotSupported)
}
return nil
}
}
if fastCtx, ok := bw.(*fasthttp.RequestCtx); ok {
fastCtx.SetBodyStreamWriter(func(bfw *bufio.Writer) {
f(ctx.Context(), input, send(fastCtx.Conn(), flusherFunc(bfw.Flush), bfw))
})
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}
// Get the flusher/deadliner from the response writer if possible.
var flusher http.Flusher
flushCheck := bw
Expand Down Expand Up @@ -164,55 +228,8 @@ func Register[I any](api huma.API, op huma.Operation, eventTypeMap map[string]an
}
}

send := func(msg Message) error {
if deadliner != nil {
if err := deadliner.SetWriteDeadline(time.Now().Add(WriteTimeout)); err != nil {
fmt.Fprintf(os.Stderr, "warning: unable to set write deadline: %v\n", err)
}
} else {
fmt.Fprintln(os.Stderr, "write deadline not supported by underlying writer")
}

// Write optional fields
if msg.ID > 0 {
bw.Write(fmt.Appendf(nil, "id: %d\n", msg.ID))
}
if msg.Retry > 0 {
bw.Write(fmt.Appendf(nil, "retry: %d\n", msg.Retry))
}

event, ok := typeToEvent[deref(reflect.TypeOf(msg.Data))]
if !ok {
fmt.Fprintf(os.Stderr, "error: unknown event type %v\n", reflect.TypeOf(msg.Data))
debug.PrintStack()
}
if event != "" && event != "message" {
// `message` is the default, so no need to transmit it.
bw.Write([]byte("event: " + event + "\n"))
}

// Write the message data.
if _, err := bw.Write([]byte("data: ")); err != nil {
return err
}
if err := encoder.Encode(msg.Data); err != nil {
bw.Write([]byte(`{"error": "encode error: `))
bw.Write([]byte(err.Error()))
bw.Write([]byte("\"}\n\n"))
return err
}
bw.Write([]byte("\n"))
if flusher != nil {
flusher.Flush()
} else {
fmt.Fprintln(os.Stderr, "error: unable to flush")
return fmt.Errorf("unable to flush: %w", http.ErrNotSupported)
}
return nil
}

// Call the user-provided SSE handler.
f(ctx.Context(), input, send)
f(ctx.Context(), input, send(deadliner, flusher, bw))
},
}, nil
})
Expand Down