1 | Extending remctl |
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2 | |
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3 | Introduction |
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4 | |
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5 | This is a guide for users and implementors of remctl who notice |
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6 | features or support currently missing and want to see how to add it, |
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7 | or who are curious which parts of remctl can be easily extended and |
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8 | which parts are more difficult. Most of the easy extensibility is on |
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9 | the server, which is written to permit straightforward addition of new |
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10 | features, particularly to the configuration and ACL files. |
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11 | |
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12 | Extension areas are presented here in roughly the order of complexity |
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13 | of additions. |
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14 | |
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15 | If you're considering extending remctl, please feel free to contact me |
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16 | at rra@stanford.edu and let me know what you're planning and what |
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17 | problem you're trying to solve. I'm generally happy to offer advice |
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18 | and incorporate and maintain extensions in the base distribution, even |
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19 | if they're optional features that require external libraries to build. |
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20 | |
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21 | ACL Methods |
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22 | |
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23 | remctl currently supports four ACL methods, but there is support in |
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24 | the ACL syntax for tagging an ACL with a new method and it's |
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25 | relatively straightforward to add new ACL methods to the server. |
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26 | |
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27 | An ACL method name may be any alphanumerics plus hyphen (-). The |
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28 | current methods are defined in server/config.c (but may be broken int |
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29 | a separate file if many more ACL methods are added). The methods |
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30 | struct defined in that file associates method names with the function |
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31 | implementing that method. |
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32 | |
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33 | To add a new ACL method, first write a function that checks a given |
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34 | user against an ACL of that method. Your function must take four |
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35 | arguments: the remote username as a string, the ACL data as a string |
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36 | (this is the part after the colon in the ACL for the current command), |
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37 | and the file and line number in the ACL for error reporting. The |
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38 | function must return CONFIG_SUCCESS if the user is authorized by that |
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39 | ACL data, CONFIG_NOMATCH if they are not, and CONFIG_ERROR on some |
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40 | sort of failure, such as failure of a remote service or a syntax error |
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41 | in the ACL data. |
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42 | |
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43 | For example, the standard acl_check_princ function which implements |
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44 | the princ ACL method does a string comparison of the ACL data to the |
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45 | remote user identity and returns CONFIG_SUCCESS if they match and |
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46 | CONFIG_NOMATCH otherwise. |
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47 | |
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48 | Once you've written that function, add it and its method name to the |
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49 | methods struct definition in server/config.c. That's all there is to |
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50 | it (although if you're submitting it for inclusion into remctl, |
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51 | documentation additions to docs/remctld.pod and either a new test |
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52 | suite or an addition to tests/server/acl-t.c would be nice). |
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53 | |
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54 | Config Options |
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55 | |
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56 | remctld configuration options are handled somewhat similarly to ACLs, |
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57 | but implementing them is likely to require more work since most new |
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58 | options will not be as self-contained in only one portion of remctld. |
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59 | But apart from implementing the effects of the option, adding a new |
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60 | option is straightforward. |
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61 | |
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62 | An option name must begin with a letter and may contain any |
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63 | alphanumerics plus hyphen (-). All options must have a value, and |
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64 | options are always written in the configuration file as |
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65 | <option>=<value>, after the command and before any ACLs. Boolean |
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66 | options should interpret "yes", "on", "true", and "1" as turning them |
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67 | on and "no", "off", "false", and "0" as turning them off. |
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68 | |
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69 | To add a new option, first write a parser for it in server/config.c. |
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70 | That function should have a name starting with option_ and will take a |
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71 | pointer to the configuration line, the value of the option as a |
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72 | string, and the name and line number of the configuration file for |
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73 | error reporting. It should return CONFIG_SUCCESS on successful |
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74 | parsing and CONFIG_ERROR on any error to parse (such as a syntax |
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75 | error). |
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76 | |
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77 | What the function does is up to you, but normally configuration |
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78 | options will add an additional member to the confline struct and the |
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79 | parser should analyze the value of the option and add the appropriate |
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80 | parsed information to the confline struct. Then, elsewhere (usually |
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81 | in server/command.c), once the command being run has been determined, |
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82 | that data can be used to do whatever the option is supposed to do. |
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83 | The members of the confline struct are defined in server/internal.h. |
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84 | |
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85 | As with ACL methods, if you submit the new option for inclusion, |
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86 | documentation for docs/remctld.pod and either a new test case or an |
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87 | addition to an existing test case are appreciated. (If you don't |
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88 | write them, I'll have to in order to incorporate the code.) |
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89 | |
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90 | Client Library |
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91 | |
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92 | The main way in which people have wanted to enhance the client library |
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93 | is to add bindings for additional programming languages. remctl now |
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94 | supports Perl, PHP, and Python, as well as a separate implementation |
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95 | in Java, but there are many other languages that could be added (Ruby, |
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96 | for example). |
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97 | |
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98 | I'm happy to include new language bindings in the main remctl |
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99 | distribution, and will also try to do the work to build packages for |
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100 | Debian and Ubuntu. Please follow the following guidelines for adding |
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101 | new language bindings: |
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102 | |
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103 | * Bindings for the C library rather than a native reimplementation in |
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104 | that language is preferred. Java is something of a special |
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105 | exception in that it's expected to run without external |
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106 | dependencies, but additional protocol implementations make for more |
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107 | maintenance work in the long run. If there are problems with the C |
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108 | interface that prevent you from using the C libraries, talk to me |
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109 | and I'll try to help. |
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110 | |
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111 | * While the interface should adjust for the language, please try to |
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112 | keep both the terminology and basics of the interface relatively |
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113 | consistent with the C library. Specifically, there should probably |
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114 | be a simple interface that runs a command and returns the result as |
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115 | an object or hash, and a more complex interface that permits sending |
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116 | multiple commands and reading the individual output, status, or |
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117 | error tokens from the server. |
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118 | |
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119 | * The C interface allows optional parameters to remctl and remctl_open |
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120 | and defaults to trying particular port numbers and principals for |
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121 | the server. Please preserve these optional parameters and defaults |
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122 | in the language bindings. |
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123 | |
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124 | * Please use the "native" way the language provides to write bindings. |
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125 | In particular, please don't use SWIG unless that's what the language |
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126 | community actively recommends. |
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127 | |
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128 | * Please include a test suite in the native module testing mechanism |
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129 | used by that language. |
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130 | |
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131 | * Language bindings should be optional and not built by default. They |
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132 | should be enabled with a --enable-<lauguage> flag to configure. See |
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133 | the existing configure logic for the languages already supported and |
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134 | the Makefile.am code for doing optional builds for examples. |
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135 | |
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136 | * The build must support building in a directory other than the source |
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137 | directory with the source files set read-only. This may mean that |
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138 | you need to copy some files from the source directory to the build |
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139 | directory if builddir != srcdir, since most language build systems |
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140 | don't support VPATH builds. See Makefile.am for how that's handled |
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141 | for existing languages and copy that setup. |
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142 | |
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143 | * Please include a README or some other documentation for users of |
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144 | that language explaining the complete interface. php/README and |
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145 | python/README are good examples. |
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146 | |
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147 | Protocol |
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148 | |
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149 | The remctl protocol is designed to be extensible by introducing a new |
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150 | protocol version. All commands come tagged with the protocol version |
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151 | required to understand them, and the server will automatically reject, |
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152 | with a version error, protocol commands with too high of a version. |
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153 | The client can also ask the server what version it supports. |
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154 | |
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155 | Currently, the protocol version is two. An initial draft of the |
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156 | changes for protocol version three is available in docs/protocol-v3, |
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157 | but may change prior to implementation. |
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158 | |
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159 | The remctl protocol is defined by docs/protocol.xml, which is |
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160 | translated into docs/protocol.txt and docs/protocl.html by xml2rfc. |
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161 | Any changes to the protocol should be documented here. |
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162 | |
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163 | I would like to keep remctl interoperable, so please talk to me before |
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164 | making changes that would modify the protocol. |
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