annotate mod_http_upload_external/README.markdown @ 2579:5e948d1392a5

mod_firewall: Add some comments
author Matthew Wild <mwild1@gmail.com>
date Sat, 25 Feb 2017 16:55:02 +0000
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1 ---
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2 description: HTTP File Upload (external service)
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3 labels: 'Stage-Alpha'
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4 ---
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5
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6 Introduction
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7 ============
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8
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9 This module implements [XEP-0363], which lets clients upload files
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10 over HTTP to an external web server.
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11
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12 This module generates URLs that are signed using a HMAC. Any web service that can authenticate
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13 these URLs can be used. There is a PHP implementation available
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14 [here](https://hg.prosody.im/prosody-modules/raw-file/tip/mod_http_upload_external/share.php). To
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15 implement your own service compatible with this module, check out the implementation notes below (and if you
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16 publish your implementation - let us know!).
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17
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18 Configuration
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19 =============
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20
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21 Add `"http_upload_external"` to modules_enabled in your global section, or under the host(s) you wish
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22 to use it on.
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23
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24 External URL
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25 ------------
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26
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27 You need to provide the path to the external service. Ensure it ends with '/'.
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28
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29 For example, to use the PHP implementation linked above, you might set it to:
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30
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31 ``` {.lua}
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32 http_upload_external_base_url = "https://your.example.com/path/to/share.php/"
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33 ```
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34
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35 Secret
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36 ------
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37
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38 Set a long and unpredictable string as your secret. This is so the upload service can verify that
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39 the upload comes from mod_http_upload_external, and random strangers can't upload to your server.
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40
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41 ``` {.lua}
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42 http_upload_external_secret = "this is a secret string!"
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43 ```
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44
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45 You need to set exactly the same secret string in your external service.
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46
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47 Limits
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48 ------
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49
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50 A maximum file size can be set by:
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51
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52 ``` {.lua}
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53 http_upload_external_file_size_limit = 123 -- bytes
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54 ```
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55
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56 Default is 100MB (100\*1024\*1024).
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57
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58 Compatibility
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59 =============
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60
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61 Works with Prosody 0.9.x and later.
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62
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63 Implementation
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64 ==============
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65
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66 To implement your own external service that is compatible with this module, you need to expose a
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67 simple API that allows the HTTP GET, HEAD and PUT methods on arbitrary URLs located on your service.
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68
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69 For example, if http_upload_external_base_url is set to `https://example.com/upload/` then your service
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70 might receive the following requests:
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71
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72 Upload a new file:
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73
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74 ```
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75 PUT https://example.com/upload/foo/bar.jpg?v=49e9309ff543ace93d25be90635ba8e9965c4f23fc885b2d86c947a5d59e55b2
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76 ```
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77
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78 Recipient checks the file size and other headers:
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79
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80 ```
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81 HEAD https://example.com/upload/foo/bar.jpg
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82 ```
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83
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84 Recipient downloads the file:
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85
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86 ```
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87 GET https://example.com/upload/foo/bar.jpg
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88 ```
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89
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90 The only tricky logic is in validation of the PUT request. Firstly, don't overwrite existing files (return 409 Conflict).
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91
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92 Then you need to validate the auth token. This will be in the URL query parameter 'v'. If it is absent, fail with 403 Forbidden.
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93
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94 Calculate the expected auth token by reading the value of the Content-Length header of the PUT request. E.g. for a 1MB file
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95 will have a Content-Length of '1048576'. Append this to the uploaded file name, separated by a space (0x20) character.
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96
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97 For the above example, you would end up with the following string: "foo/bar.jpg 1048576"
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98
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99 The auth token is a SHA256 HMAC of this string, using the configured secret as the key. E.g.
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100
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101 ```
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102 calculated_auth_token = hmac_sha256("foo/bar.jpg 1048576", "secret string")
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103 ```
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104
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105 If this is not equal to the 'v' parameter provided in the upload URL, reject the upload with 403 Forbidden.
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106
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107 Note: your language/environment may provide a function for doing a constant-time comparison of these, to guard against
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108 timing attacks that may be used to discover the secret key.