testscript: add waitmatch command #268
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It blocks until a background process prints a matching line to stdout. Any given env var names are set to the subexpression strings as well. This is useful to wait for a background process to be ready before running more commands to interact with it, such as waiting for an HTTP server to listen on a TCP port before sending it the first request. In fact, our interrupt tests already had this problem; we only worked around it by having the process create a file when it's ready, and adding a custom command which would wait for the file by polling. It's much nicer and faster to use waitmatch instead, and as a bonus, we can refactor existing tests rather than adding more.
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Note that I went with |
| // which matches the given regular expression. Once a match is found, the given | ||
| // environment variable names are set to the subexpressions of the match. | ||
| func (ts *TestScript) cmdWaitMatch(neg bool, args []string) { | ||
| if len(args) < 1 { |
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| if len(args) < 1 { | |
| if len(args) < 2 { |
| cmd.Stdin = strings.NewReader(ts.stdin) | ||
| cmd.Stdout = &stdoutBuf | ||
| stdoutr, stdoutw, err := os.Pipe() |
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Also, I'm not sure that os.Pipe is good enough here. If the process is producing a lot of output and the script never calls waitmatch, the pipe buffer could fill up and then the process will be blocked and potentially non-functioning as a result. I suspect we need to write everything to a buffer immediately, and then have a way to layer a reader on top of that.
Also, I wonder if we should make it possible to wait on stderr matches too? It's common for logged output to be printed to stderr and probably not uncommon to need to wait on that. Maybe waitmatch should wait on the combined output, although that might be tricky to arrange because we also need it to be split.
| } | ||
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| // readLine consumes enough bytes to read a line. | ||
| func readLine(r io.Reader) ([]byte, error) { |
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I don't get why we need to use this rather than (say) bufio.Scanner.
(see commit message)