How to handle streaming responses in a golang http client
Jul 04, 2025 am 01:35 AM
To handle streaming responses of HTTP clients in Go, follow the following steps: 1. Initiate a GET request and disable automatic processing of the response body; 2. Use resp.Body to read block by block rather than load memory at one time; 3. Text data can be processed by line by line with bufio.Scanner; 4. Binary or large files should be read and written to disk while reading; 5. Always defer resp.Body.Close() to avoid leakage; 6. Set timeout or active interruption requests in combination with context.Context; 7. Pay attention to details such as middleware buffering and parsing JSON segment by segment. Various streaming responses can be handled efficiently by these methods.
It is not difficult to handle streaming responses to HTTP clients in Go, but some basic mechanisms need to be understood. The key is not to read the entire response body into memory at one time, but to read it step by step in streaming.
Basic processing method of streaming response
When you initiate an HTTP request and expect the server to return data that is continuously sent (such as Event Stream or large file download), you need to set the request method of http.Client to GET and disable redirection or automatically process the response body.
Go's standard library will load all response bodies into memory by default unless you manually specify that you don't. The correct way is to use resp, err := client.Do(req) to get the response, do not call ioutil.ReadAll(resp.Body) , but directly operate resp.Body , io.ReadCloser .
For example:
req, _ := http.NewRequest("GET", "http://example.com/stream")
client := &http.Client{}
resp, err := client.Do(req)
if err != nil {
log.Fatal(err)
}
defer resp.Body.Close()
scanner := bufio.NewScanner(resp.Body)
for scanner.Scan() {
fmt.Println("Received line:", scanner.Text())
} This code reads the response content line by line through bufio.Scanner , which is very suitable for processing text-type streaming data.
Handle binary streams or large files
If you are receiving binary streams or large files such as pictures and videos, you can no longer read them by line. At this time, you should use io.Copy or block reading to write to local files or other output streams.
For example, save a growing large file:
outFile, err := os.Create("output.bin")
if err != nil {
log.Fatal(err)
}
defer outFile.Close()
_, err = io.Copy(outFile, resp.Body)
if err != nil {
log.Fatal(err)
}This method does not load the entire file into memory, but writes the disk while reading and writing, which is suitable for handling very large response bodies.
A few points to note:
- Always remember to call
defer resp.Body.Close(), otherwise it is easy to cause connection leakage. - If the server does not set the appropriate
Content-Length, you may need to determine yourself when the stream will end. - Use
context.Contextto set the timeout or cancel mechanism to avoid long-term hangs.
Error handling and interrupt control
Streaming responses usually last longer, so error handling is especially important. In addition to checking whether there are errors in each read, network interruption, server shutdown, etc. should also be considered.
You can combine context.WithCancel to actively interrupt the stream:
ctx, cancel := context.WithCancel(context.Background()) req = req.WithContext(ctx) // Call cancel() after a certain condition is triggered cancel()
This allows you to proactively terminate the request externally, rather than passively waiting for the server to close the connection.
Also, pay attention to the following common questions:
- Some middleware or proxy may buffer streaming data, causing the client to not see real-time results.
- If the stream contains JSON data, it is recommended to parse segment by segment, rather than accumulate into a complete string before processing.
Basically that's it. By mastering these points, you can flexibly handle various streaming HTTP responses in Go.
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