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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 unique ID 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 +id <String> // The Unique ID for this post
160 ```
161
162 Given that posts won't come in at a high enough rate, and that the
163 purpouse is only to help feed readers identify each unique piece of
164 content, for this version the `id` will be the same number as the
165 `publishedOn`.
166
167 ## The Generator Interface
168
169 Every generator must implement this interface in order to work with
170 Blog.
171
172 * Generators MUST be a function
173 * Generators SHOULD read the source, destination, and posts parameters to
174 write files.
175 * Generators MUST NOT write anything into the source directory
176 * Generators MUST return a promise
177 * Generators SHOULD NOT resolve the promise with any information, as it will
178 be discarded
179 * Generators MUST throw exceptions if they encounter an unrecoverable error
180
181 ```
182 IGenerator(source<String>, destination<String>, posts<Array<String>>) => Promise
183 ```
184
185 ## New Generators
186
187 ### Static Generator
188
189 This generator will have the logic to move static assets around. It will
190 re-use the current asset logic in the `#_generate` method in Blog.
191
192 ```
193 StaticGenerator <IGenerator>
194 ```
195
196 ### HTML Generator
197
198 This generator will have the logic to generate an HTML file. It will
199 re-use the current HTML logic in the `#_generate` method in Blog.
200
201 ```
202 HTMLGenerator <IGenerator>
203 ```
204
205 ### RSS Generator
206
207 This generator will have the logic to generate an RSS file. It will
208 re-use the current HTML logic in the `#_generate` method in Blog,
209 however, instead of using the `index.html` template it will use a
210 `feed.xml` template that generates a valid RSS 2.0 feed document.
211
212 ```
213 RSSGenerator <IGenerator>
214 ```
215
216 ## Modifications to existing parts of the code
217
218 The `#_generate` function will be modified so it will now parse the
219 post markdown, and then iterate over the generators, calling them
220 so they create the appropriatet files.
221
222 ## Important Metrics
223
224 Given we're only processing 3 blog posts, and this is a compile time
225 activity and not runtime, there are no recommended metrics in terms
226 of file throughput performance or runtime performance.
227
228 This should change if this would ever handle a higher volume, or would
229 be expected to run this process runtime.
230
231 ## Furhter Improvements
232
233 It's recommended to eventually put more effort in assigning a unique ID
234 to each post so we can use more feed formats.
235
236 For more compatibility and future proofing, the same solution for
237 RSS could be used to generate other feed formats, just adding
238 a new generator
239
240 This same solution could be extended to serve the blog in different formats
241 (eg. a .txt that is easy to read in terminals)