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[rbdr/blog] / doc / specs / 20200601-serving-different-versions.md
1 # Problem
2
3 Feed reader users should be able to subscribe to the blog
4
5 # Background
6
7 As of this writing, the blog is served as HTML which is appropriate for
8 web browsers but maybe not for other mechanisms like feed readers.
9
10 Feed readers have different formats that they support:
11 * h-feed is a microformat built into the page
12 * rss and atom are XML based publishing formats
13 * JSON feed is a JSON based publishing format
14 * rss 3.0 is a text based pblishing format :P
15
16 Currently the blog contains a single generator function that copies
17 assets and generates HTML out of markdown files. This is good enough for
18 the current setup, but if it were to generate more it would get messy
19 real quick.
20
21 Given the constraints listed below, some formats are not recommended:
22 * RSS 3.0 is not a good candidate at the moment as it would require
23 us to parse the markdown to extract the title.
24 * Atom would work, however, given the requirement for an id, title, and
25 date this would require more effort than a more lenient format.
26 * RSS 2.0 fits the constraints as we wouldn't need to specify anything
27 for the item.
28 * JSON Feed would work, however given the requirement for an id, thtis
29 would require more effort than a more lenient format.
30
31 It is unclear whether the current constraints are good enough for feed
32 readers. If this causes issues, it's likely we will have to include date,
33 id or title as required in the other formats.
34
35 After reviewing the functionality of existing readers, it has been found
36 that an id and publication date would be needed for readers to behave
37 correctly. This means that ATOM and JSON Feed would be equally valid
38 as solutions than RSS 2.0
39
40 The current generator function depends on knowing a source for the post
41 being generated, and a target on where the assets will be placed.
42
43 # Hypothesis
44
45 Given we serve the blog in a feed reader friendly format, users will be able to subscribe.
46
47 # Test of Hypothesis
48
49 Given I add the blog to a feed reader service like Reeder or Feedly, I will be able to see the entries.
50 Given I add a new entry to the blog, the entries will be updated.
51
52 # Assumptions
53
54 * We can generate a valid feed with just the entries themselves and the existing
55 blog data.
56 * We can: Validated by generating an example file.
57 * Including just a list of items with the whole content is good enough for
58 feed readers.
59 * We can't: It seems like we'll require at least a guid. The old reader
60 behaves correctly with just the guid. It's unclear whether feedly
61 does since it has caching. Will leave grok running.
62 * It isn't required to link back, and we can include the whole text.
63 * This is correct, however it might make sense to just link to the
64 blog itself.
65
66 # Constraints
67
68 * We won't be parsing the markdown to generate feed items.
69 * We won't be adding any sort of frontmatter to the entries.
70 * The blog will remain ephemeral, and we won't introduce permalinks.
71 * We won't have configurable templating or options to add/remove
72 output types.
73
74 # Solution Proposal
75
76 We will add a new step in the creation process to create metadata for the
77 post that will allow each post to be uniquely identified, as well as
78 having a publish date related to them.
79
80 We will split the current generator function into generators, and create
81 a new generator that will generate an RSS 2.0 file
82
83 # Blackbox
84
85 ```
86 ╔══════════════════════╗
87 ║ When Adding a Post ║
88 ╚══════════════════════╝
89 ┌───────────────┐ ┌───────────────┐
90 │ │ │ │
91 ┌────────────────▶│ writeMetadata │─────────▶│ Metadata File │
92 │ │ │ │ │
93 │ └───────────────┘ └───────────────┘
94
95
96 │ ╔════════════════════════╗
97 │ ║ When Generating Output ║
98 │ ╚════════════════════════╝
99 │ ┌─────────────────┐ ┌───────────────┐
100 │ │ │ │ │
101 │ ┌─────▶│ StaticGenerator │───────▶│ Static Assets │
102 │ │ │ │ │ │
103 │ │ └─────────────────┘ └───────────────┘
104 ┌───────┐ │ ┌───────────────┐ ┌───────────┐
105 │ │ │ │ │ │ │
106 │ Blog │──────┼─────▶│ HTMLGenerator │─────────▶│ HTML File │
107 │ │ │ │ │ │ │
108 └───────┘ │ └───────────────┘ └───────────┘
109 │ ┌──────────────┐ ┌──────────┐
110 │ │ │ │ │
111 └─────▶│ RSSGenerator │──────────▶│ RSS File │
112 │ │ │ │
113 └──────────────┘ └──────────┘
114 ```
115
116 # Theory of Operation
117
118 ## When Adding a Post
119
120 When the add function of the blog is triggered, it will shift the posts
121 as it currently does and then will generate a new UUID and take the
122 current timestamp. This will be saved in a JSON file in the output
123 directory called "metadata.json"
124
125 ## When Generating Output
126
127 When the generate function of the blog is triggered, it will iterate
128 over every post. For each of them it will parse the markdown content,
129 and the metadata, creating an object of type `tPost` and pushing it
130 to an array.
131
132 Next, it will iterate from a list of generator functions and call them
133 with the source and target directories, and an array containing the `tPost`
134 objects. Each generator function will do its work, throwing an exception
135 if they encounter an error.
136
137 When the static generator is called, it will remove the current assets
138 directory in the target directory, and recursively copy the assets from
139 the source directory.
140
141 When the HTML generator is called, it will parse an `html` template, using
142 the posts as the context, and will place the resulting file in the target
143 directory.
144
145 When the RSS generator is called, it will parse an `rss` template, using
146 the posts as the context, and will place the resulting file in the target
147 directory.
148
149 # Technical Specification
150
151 ## The Post Data Structure
152
153 This spec introduces a data structure to help generate output.
154
155 ```
156 tPost <Object>
157 +html <String> // The markup of the post
158 +publishedOn <Number> // The timestamp when this post was added
159 +uuid <String> // The UUID for this post
160 ```
161
162 ## The Generator Interface
163
164 Every generator must implement this interface in order to work with
165 Blog.
166
167 * Generators MUST be a function
168 * Generators SHOULD read the source, destination, and posts parameters to
169 write files.
170 * Generators MUST NOT write anything into the source directory
171 * Generators MUST return a promise
172 * Generators SHOULD NOT resolve the promise with any information, as it will
173 be discarded
174 * Generators MUST throw exceptions if they encounter an unrecoverable error
175
176 ```
177 IGenerator(source<String>, destination<String>, posts<Array<String>>) => Promise
178 ```
179
180 ## New Generators
181
182 ### Static Generator
183
184 This generator will have the logic to move static assets around. It will
185 re-use the current asset logic in the `#_generate` method in Blog.
186
187 ```
188 StaticGenerator <IGenerator>
189 ```
190
191 ### HTML Generator
192
193 This generator will have the logic to generate an HTML file. It will
194 re-use the current HTML logic in the `#_generate` method in Blog.
195
196 ```
197 HTMLGenerator <IGenerator>
198 ```
199
200 ### RSS Generator
201
202 This generator will have the logic to generate an RSS file. It will
203 re-use the current HTML logic in the `#_generate` method in Blog,
204 however, instead of using the `index.html` template it will use a
205 `feed.xml` template that generates a valid RSS 2.0 feed document.
206
207 ```
208 RSSGenerator <IGenerator>
209 ```
210
211 ## Modifications to existing parts of the code
212
213 The `#_generate` function will be modified so it will now parse the
214 post markdown, and then iterate over the generators, calling them
215 so they create the appropriatet files.
216
217 ## Important Metrics
218
219 Given we're only processing 3 blog posts, and this is a compile time
220 activity and not runtime, there are no recommended metrics in terms
221 of file throughput performance or runtime performance.
222
223 This should change if this would ever handle a higher volume, or would
224 be expected to run this process runtime.
225
226 ## Furhter Improvements
227
228 It's recommended to eventually put more effort in assigning a unique ID
229 to each post so we can use more feed formats.
230
231 For more compatibility and future proofing, the same solution for
232 RSS could be used to generate other feed formats, just adding
233 a new generator
234
235 This same solution could be extended to serve the blog in different formats
236 (eg. a .txt that is easy to read in terminals)