[WIP] Fix race condition in HTTP request sending

[Copilot]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

Original prompt

Problem

Issue #1 identifies a race condition where the HTTP request goroutine can start sending before the multipart writer goroutine begins writing data. This can result in the server observing an empty or effectively empty multipart file part, even though the counters usually show the right values.

Root Cause

In internal/httprequest/multipart.go, the Send() method:

1. Creates an io.Pipe()
2. Launches a goroutine to write multipart data
3. Immediately calls r.sendRequest() to send the HTTP request

There's no synchronization to ensure the writer goroutine has started and begun writing before the HTTP request is initiated. This creates a race condition where:

• The HTTP request can complete before any data is written to the pipe
• The server may read an empty body
• Early errors in the writer goroutine aren't caught before sending the request

Solution Requirements

Implement synchronization to ensure:

1. The writer goroutine has started successfully
2. At least the multipart headers and first field/file part header have been written to the pipe
3. Any early errors in the writer goroutine are caught and returned before the HTTP request begins
4. The pipe reader will have data available when the server starts reading
5. Add timeout handling to prevent deadlock
6. Properly propagate errors from the writer goroutine

Implementation Details

Modify internal/httprequest/multipart.go:

1. Add a buffered channel to signal when the writer goroutine is ready
2. Have the writer goroutine signal readiness after successfully creating at least the first field/file part header
3. Wait for the ready signal before calling sendRequest()
4. Handle timeout scenarios to prevent deadlock
5. Ensure all error paths properly signal the ready channel

Files to Modify

• internal/httprequest/multipart.go - Add synchronization to Send() method

Testing

Ensure existing tests pass, particularly:

• internal/httprequest/multipart_test.go
• examples/multipart_streaming_example/main_test.go

The solution should maintain backward compatibility and not break existing streaming functionality.

Related Issue

Fixes #1

This pull request was created from Copilot chat.

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