git.r.bdr.sh - rbdr/blog/blob - 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)