textproto.go

     1  // Copyright 2010 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Package textproto implements generic support for text-based request/response
     6  // protocols in the style of HTTP, NNTP, and SMTP.
     7  //
     8  // The package provides:
     9  //
    10  // [Error], which represents a numeric error response from
    11  // a server.
    12  //
    13  // [Pipeline], to manage pipelined requests and responses
    14  // in a client.
    15  //
    16  // [Reader], to read numeric response code lines,
    17  // key: value headers, lines wrapped with leading spaces
    18  // on continuation lines, and whole text blocks ending
    19  // with a dot on a line by itself.
    20  //
    21  // [Writer], to write dot-encoded text blocks.
    22  //
    23  // [Conn], a convenient packaging of [Reader], [Writer], and [Pipeline] for use
    24  // with a single network connection.
    25  package textproto
    26  
    27  import (
    28  	"bufio"
    29  	"fmt"
    30  	"io"
    31  	"net"
    32  )
    33  
    34  // An Error represents a numeric error response from a server.
    35  type Error struct {
    36  	Code int
    37  	Msg  string
    38  }
    39  
    40  func (e *Error) Error() string {
    41  	return fmt.Sprintf("%03d %s", e.Code, e.Msg)
    42  }
    43  
    44  // A ProtocolError describes a protocol violation such
    45  // as an invalid response or a hung-up connection.
    46  type ProtocolError string
    47  
    48  func (p ProtocolError) Error() string {
    49  	return string(p)
    50  }
    51  
    52  // A Conn represents a textual network protocol connection.
    53  // It consists of a [Reader] and [Writer] to manage I/O
    54  // and a [Pipeline] to sequence concurrent requests on the connection.
    55  // These embedded types carry methods with them;
    56  // see the documentation of those types for details.
    57  type Conn struct {
    58  	Reader
    59  	Writer
    60  	Pipeline
    61  	conn io.ReadWriteCloser
    62  }
    63  
    64  // NewConn returns a new [Conn] using conn for I/O.
    65  func NewConn(conn io.ReadWriteCloser) *Conn {
    66  	return &Conn{
    67  		Reader: Reader{R: bufio.NewReader(conn)},
    68  		Writer: Writer{W: bufio.NewWriter(conn)},
    69  		conn:   conn,
    70  	}
    71  }
    72  
    73  // Close closes the connection.
    74  func (c *Conn) Close() error {
    75  	return c.conn.Close()
    76  }
    77  
    78  // Dial connects to the given address on the given network using [net.Dial]
    79  // and then returns a new [Conn] for the connection.
    80  func Dial(network, addr string) (*Conn, error) {
    81  	c, err := net.Dial(network, addr)
    82  	if err != nil {
    83  		return nil, err
    84  	}
    85  	return NewConn(c), nil
    86  }
    87  
    88  // Cmd is a convenience method that sends a command after
    89  // waiting its turn in the pipeline. The command text is the
    90  // result of formatting format with args and appending \r\n.
    91  // Cmd returns the id of the command, for use with StartResponse and EndResponse.
    92  //
    93  // For example, a client might run a HELP command that returns a dot-body
    94  // by using:
    95  //
    96  //	id, err := c.Cmd("HELP")
    97  //	if err != nil {
    98  //		return nil, err
    99  //	}
   100  //
   101  //	c.StartResponse(id)
   102  //	defer c.EndResponse(id)
   103  //
   104  //	if _, _, err = c.ReadCodeLine(110); err != nil {
   105  //		return nil, err
   106  //	}
   107  //	text, err := c.ReadDotBytes()
   108  //	if err != nil {
   109  //		return nil, err
   110  //	}
   111  //	return c.ReadCodeLine(250)
   112  func (c *Conn) Cmd(format string, args ...any) (id uint, err error) {
   113  	id = c.Next()
   114  	c.StartRequest(id)
   115  	err = c.PrintfLine(format, args...)
   116  	c.EndRequest(id)
   117  	if err != nil {
   118  		return 0, err
   119  	}
   120  	return id, nil
   121  }
   122  
   123  // TrimString returns s without leading and trailing ASCII space.
   124  func TrimString(s string) string {
   125  	for len(s) > 0 && isASCIISpace(s[0]) {
   126  		s = s[1:]
   127  	}
   128  	for len(s) > 0 && isASCIISpace(s[len(s)-1]) {
   129  		s = s[:len(s)-1]
   130  	}
   131  	return s
   132  }
   133  
   134  // TrimBytes returns b without leading and trailing ASCII space.
   135  func TrimBytes(b []byte) []byte {
   136  	for len(b) > 0 && isASCIISpace(b[0]) {
   137  		b = b[1:]
   138  	}
   139  	for len(b) > 0 && isASCIISpace(b[len(b)-1]) {
   140  		b = b[:len(b)-1]
   141  	}
   142  	return b
   143  }
   144  
   145  func isASCIISpace(b byte) bool {
   146  	return b == ' ' || b == '\t' || b == '\n' || b == '\r'
   147  }
   148  
   149  func isASCIILetter(b byte) bool {
   150  	b |= 0x20 // make lower case
   151  	return 'a' <= b && b <= 'z'
   152  }
   153
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