upstream-mattermost/api/v4/source/reactions.yaml

  /api/v4/reactions:
    post:
      tags:
        - reactions
      summary: Create a reaction
      description: |
        Create a reaction.
        ##### Permissions
        Must have `read_channel` permission for the channel the post is in.
      operationId: SaveReaction
      requestBody:
        content:
          application/json:
            schema:
              $ref: "#/components/schemas/Reaction"
        description: The user's reaction with its post_id, user_id, and emoji_name fields
          set
        required: true
      responses:
        "201":
          description: Reaction creation successful
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/Reaction"
        "400":
          $ref: "#/components/responses/BadRequest"
        "403":
          $ref: "#/components/responses/Forbidden"
  "/api/v4/posts/{post_id}/reactions":
    get:
      tags:
        - reactions
      summary: Get a list of reactions to a post
      description: |
        Get a list of reactions made by all users to a given post.
        ##### Permissions
        Must have `read_channel` permission for the channel the post is in.
      operationId: GetReactions
      parameters:
        - name: post_id
          in: path
          description: ID of a post
          required: true
          schema:
            type: string
      responses:
        "200":
          description: List reactions retrieve successful
          content:
            application/json:
              schema:
                type: array
                items:
                  $ref: "#/components/schemas/Reaction"
        "400":
          $ref: "#/components/responses/BadRequest"
        "401":
          $ref: "#/components/responses/Unauthorized"
        "403":
          $ref: "#/components/responses/Forbidden"
  "/api/v4/users/{user_id}/posts/{post_id}/reactions/{emoji_name}":
    delete:
      tags:
        - reactions
      summary: Remove a reaction from a post
      description: |
        Deletes a reaction made by a user from the given post.
        ##### Permissions
        Must be user or have `manage_system` permission.
      operationId: DeleteReaction
      parameters:
        - name: user_id
          in: path
          description: ID of the user
          required: true
          schema:
            type: string
        - name: post_id
          in: path
          description: ID of the post
          required: true
          schema:
            type: string
        - name: emoji_name
          in: path
          description: emoji name
          required: true
          schema:
            type: string
      responses:
        "200":
          description: Reaction deletion successful
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/StatusOK"
        "400":
          $ref: "#/components/responses/BadRequest"
        "401":
          $ref: "#/components/responses/Unauthorized"
        "403":
          $ref: "#/components/responses/Forbidden"