Prefix error messages with package name

[emersion]

This makes it easier to track down where errors come from.

[coveralls]

Coverage remained the same at 91.222% when pulling d292723f48413a3e228000da00343f09b9f708bd on emersion:error-prefix into fbefd10859f2cba1f6af048b259f4568a17aa83c on pires:master.

[emersion]

The confusion mainly comes from e.g. net.Conn.Read suddenly returning the error "Invalid address". Since I'm not calling explicitly a proxyproto function (the method is hidden behind an interface, and called far away from the proxyproto.Listener setup), figuring out what happens is complicated.

This is also a pattern used throughout the standard Go library.

[pires]

Would you be so kind to link me an example in the Go std library so I can learn?

[emersion]

A few examples found by grepping:

src/archive/tar/common.go
30: ErrHeader          = errors.New("archive/tar: invalid tar header")
31: ErrWriteTooLong    = errors.New("archive/tar: write too long")
32: ErrFieldTooLong    = errors.New("archive/tar: header field too long")
33: ErrWriteAfterClose = errors.New("archive/tar: write after close")
34: errMissData        = errors.New("archive/tar: sparse file references non-existent data")
35: errUnrefData       = errors.New("archive/tar: sparse file contains unreferenced data")
36: errWriteHole       = errors.New("archive/tar: write non-NUL byte in sparse hole")
631:        return nil, errors.New("archive/tar: FileInfo is nil")
src/bytes/reader.go
54:     return 0, errors.New("bytes.Reader.ReadAt: negative offset")
80:     return errors.New("bytes.Reader.UnreadByte: at beginning of slice")
106:        return errors.New("bytes.Reader.UnreadRune: at beginning of slice")
109:        return errors.New("bytes.Reader.UnreadRune: previous operation was not ReadRune")
128:        return 0, errors.New("bytes.Reader.Seek: invalid whence")
131:        return 0, errors.New("bytes.Reader.Seek: negative position")
src/crypto/cipher/gcm.go
113:        return nil, errors.New("cipher: incorrect tag size given to GCM")
117:        return nil, errors.New("cipher: the nonce can't have zero length, or the security of the key will be immediately compromised")
125:        return nil, errors.New("cipher: NewGCM requires 128-bit block cipher")
195:var errOpen = errors.New("cipher: message authentication failed")
src/crypto/tls/conn.go
603:        return c.in.setErrorLocked(errors.New("tls: internal error: attempted to read record with pending application data"))
762:        return c.in.setErrorLocked(errors.New("tls: too many ignored records"))
1073:   errClosed   = errors.New("tls: use of closed connection")
1074:   errShutdown = errors.New("tls: protocol is shutdown")
1137:       return errors.New("tls: internal error: unexpected renegotiation")
1166:       return errors.New("tls: unknown Renegotiation value")
1194:       return c.in.setErrorLocked(errors.New("tls: too many non-advancing records"))
1316:var errEarlyCloseWrite = errors.New("tls: CloseWrite called before handshake complete")
1372:       c.handshakeErr = errors.New("tls: internal error: handshake should have had a result")
1429:       return errors.New("tls: VerifyHostname called on TLS server connection")
1432:       return errors.New("tls: handshake has not yet been performed")
1435:       return errors.New("tls: handshake did not verify certificate chain")
src/mime/mediatype.go
107:        return errors.New("mime: no media type")
113:        return errors.New("mime: expected slash after first token")
117:        return errors.New("mime: expected token after slash")
120:        return errors.New("mime: unexpected content after media subtype")
128:var ErrInvalidMediaParameter = errors.New("mime: invalid media parameter")
190:            return "", nil, errors.New("mime: duplicate parameter name")

… And so on…

[pires]

I'm lazy! Thanks for the lesson learned. Will you want to do the same for the tlvparse package?

[emersion]

Sure, will do!

[emersion]

Actually, unless I'm mistaken, it doesn't seem like tlvparse creates any new error values. It just re-uses proxyproto errors.